Policing the cheaters


2a) Most people speak of "sanity checking" with software as perfectly acceptable
I don't know who "most" are, but my impression from reading dozens of these threads each year is that most people are quite clear that any engine use on a game in progress is cheating. Checking to see if an oponent is cheating during a game is best left to the arbiters--Erik for this site.
As for those that find this thread tiresome, reading is optional. These discussions are endemic to online chess.

2a) Most people speak of "sanity checking" with software as perfectly acceptable
I don't know who "most" are, but my impression from reading dozens of these threads each year is that most people are quite clear that any engine use on a game in progress is cheating.
I can only give you what my experiences are in the other couple of cheating threads I've read. Each time 'sanity checking' was mentioned it wasn't addressed as cheating (which surprised and disappointed me).
Personally, having a computer do any sort of analysis means you're trying to gain an unfair advantage over your opponent. This includes using computer databases as the chess.com rules allow, in my opinion.
For an example on how powerful simply using databases can be, copy and paste the first 8 moves or so from your next game into a word processor. Remove all the line breaks so it appears as an unbroken stream of moves in the form of one sentence. Paste that into Google. If you're not a master of openings, watch your openings improve 100x while you simply plug in the grandmaster game you find where someone else did the same thing.
According to chess.com - completely legal - since you found it in an on-line database. In my humble opinion, you're not playing if you're doing that, though. You're copying Kasparov (or Karpov, or Fischer, or whoever).

I wear a special hat made of cheater deterring aluminum foil when i play chess.
i've played 69 games so far.
36 of them are fools, 23 of them are cheaters, and 10 of them are very very good at playing chess. The trend is changing though. When i first started playing on-line chess, everyone was cheating. i then wasted some time learning about opening principles, endgame tactics, and positional play. something happened while i was distracted and the number of cheaters decreased.
Cheaters beware! chess.com is documenting your every move and turning over the records to the DHS. you will be placed on the no-fly list and you will suffer much inconvenience at the airport.

neospooky> 'sanity checking' was mentioned it wasn't addressed as cheating
On chess.com any 'sanity checking' with a chess engine, and use of a chess engine at all to aid your play, is cheating.
eternal21> or database search you cheat.
On chess.com a database search is not cheating.
We may personally feel the rules should be different, but what is and is not cheating on chess.com is well-defined by the rules posted above.
For an example on how powerful simply using databases can be, copy and paste the first 8 moves or so from your next game into a word processor. Remove all the line breaks so it appears as an unbroken stream of moves in the form of one sentence. Paste that into Google. If you're not a master of openings, watch your openings improve 100x while you simply plug in the grandmaster game you find where someone else did the same thing.
Too much work. I click on the "get PGN" button underneath the game score, save it to my hard drive, then open it in ChessBase, or Chess Informant Expert, or similar software where I can begin my database study. It makes this sort of chess an excellent way to try new opening ideas and learn them well. However, such database use is time intensive, and I do not work that hard in every game. More often I play the same lousy moves I'll play in OTB or online blitz, with the same abyssmal results.
Books and databases are a well established tradition and alluring feature of coorespondence chess. Alas, these turn-based website have brought hundreds of thousands of newbies (who never played through postcards) into slow chess, and many of them are unacquainted with the form of play, erroneously assuming it to be just like face to face at the club (where in truth I offer dozens of take-backs as we look for the ideas of the position).
Engine use is banned at most of these sites, but is permitted in some correspondence chess.

neospooky> 'sanity checking' ... wasn't addressed as cheating
On chess.com any 'sanity checking' with a chess engine, and use of a chess engine at all to aid your play, is cheating.
Just wanted to address an egregious misquote - I know using any engine is cheating. I was speaking specifically about how it was discussed (or rather, not discussed) in the other threads I'd read recently.
Well, judging from all the responses I have come to the conclusion that there is no definite way to tell if you are playing someone that is using a chess engine to make their moves.
You can suspect strongly that they are cheating but you won't know for sure. Even if they tell you they are then there is no way to know for sure that they aren't just saying as much.
Because there is no way to ascertain for certain that someone is cheating is it fair to punish a suspected cheater?

I agree with you Erik, I believe you can tell...I played a guy that says he is 13 and just started playing but his moves were too good IMO.
To me it looked as though he was using a chess engine but I wasn't sure so I let it slide. Should I report it?

On top of that, in the grand scheme of things, is it even that important? Your chess.com rating can't be used anywhere. It doesn't get you a t-shirt or advanced tournament standing.
Oh, no! I wish a T-shirt! Something with "chess.com 2000+" or so! Erik, pleeeease, can't you arange it?

Earlengray> while in turn based chess even this can be fooled
Yup. Besides that, I often leave a game board open while analyzing an entirely different position in Chessbase... and it would mean running some rather invasive software. ;)

According to chess.com - completely legal - since you found it in an on-line database. In my humble opinion, you're not playing if you're doing that, though. You're copying Kasparov (or Karpov, or Fischer, or whoever).
You are wrong - it is a part of chess. There are >1000 GMs in the word today, and hundreds of top-players through history - yuo need not to investigate all from the first move!
Every master in OTB, CC or on-line chess do it - copying great examples. Fresh ideas in opening are rare. A difference is that in OTB game you need to have all it in your head - so you need to have an excelent memory to be a master. In our way of play, you can use "external memory" (databases and books); however, CPU need to be your own!
And in every game you wil come "out of books" at some points, usually between 10th and 15th move. If you, in the first phase of the game, only coppy moves, you dont understand ideas and probably you will lose in midlegame agaist an experienced oponent. You need to study openings all the time, and search for new ideas.
I published here some of my games, with notes when we run out of the theory. Sometimes I prepared news in advance (before the game), sometimes during the game. Or, of course, I am faced with a novelty during the game and need to demonstrate I understand basic ideas of the position.
A sharp draw in Frehch Defence (Gonnosuke vs LydiaBlonde
His move 13. Qbt5!? was a news (at least acording to chessok.com and chesslive.de). It was followed by an interesting strugle, resulted in a draw.
A strugle for the center (learn from Rusa Goletiani!)
Her 11. Bb3!? was a news. I answered with a combination of ideas from few other games, wich I found in databases. I lost, and this game (as the previous one!) could be included in databases, for future users - maybe they will find something better!
French defence - a game of interest for theory
This is the nice one! In the databases, I found 6 games with a position after 12th move of black - and in all of them black win! In analysis (and I am not sure now was it before the game or after it's begining) I found a new idea for white (moves 13 to 16th). And I win! Smart me!
I have no so good memory to can have all this in my head. So, this kind of chess (as like as clasical CC) alow me to crate much beter games, which can be of interest for others too! (And become a parto of "theory".)

Extremely good point.

"More often I play the same lousy moves I'll play in OTB or online blitz, with the same abyssmal results."
Now THAT's cheating!
I own the patent.

A man with one clock knows what time it is, but a man with two clocks is playing chess.
A man with two clocks is also never certain of the time.