Gambits...which to take and which to decline

I have to beg to differ with one of them.  The Milner-Barry Gambit should be accepted!

After 1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Qb6 (4...Nc6 is also possible, but developing the Queen first avoids the 5.Be3 line) 5.Nf3 Nc6 6.Bd3?! (Yes, it really is dubious - 6.a3! Is best) 6...cxd4 (6...Bd7? 7.dxc5! With advantage to White) 7.cxd4 Bd7! (7...Nxd4? 8.Nxd4 Qxd4?? 9.Bb5+ +-) 8.O-O (8.Bc2?! Nb4! Is also better for Black) 8...Nxd4! 9.Nxd4 (9.Ng5 and 9.Nbd2 can be tricky if Black does not know then, but both are better for Black with correct play) 9...Qxd4 10.Nc3 a6! With a slight advantage to Black!

8. be2 keeps the pawn though no? Seems equal after that instead of castling

8.Be2 is a complete waste of time for White.  Why did you play 6.Bd3 in the first place?  You are now a full tempo down compared to the 6.Be2 line!  Black is better!  At least after 6.Be2, you maintain equality.  Not as good as 6.a3!, but better than wasting time with 6.Bd3 just to then play 8.Be2.

This is a new gambit I'm trying out

Always accept if you want to refute. How can being a pawn up be wrong as long as you are not greedy. The advantage of being material up is that you can give it back at any time.

I don't see the compensation. Just bxb5 and how does black continue?

not always, sometimes your opponent makes an awkward position during a gambit, so sometimes if you decline, your opponent will still have a weird (and a bit worse) of a position while you didn't do anything. Additionally, you might be playing into your opponents prep if you accept. So, yeah

A good example is the Janzen-Korchnoi gambit in the Dutch. (h3 g4) Accepting the pawn is probably worse for Black than simply ignoring it and developing. Obviously other examples like the Blackburne-Shilling are widely known. The only way to refute is to decline the pawn and it is an easily refuted opening.

Of course it depends on the position, but as a general rule you may want to:

- accept the gambit if you want to refute it or learn something new.

- decline the gambit if you don't know it.

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if you accept the vienna gambit then you're in a much worse position already

Declining KG is fine, so long as you don't do anything weird like the Panteldakis Countergambit 

Accepting the Urusov is fine

Gunderam Gambit !

My general rule is accept all gambits except Queen's (which is not a true gambit), then triple your concentration looking for traps and exploits. Quickly develop your pieces. Most gambits are fundamentally unsound, so the best way to play against them is to accept them. 

My general rule don't accept the gambit but offer up a countergambit of your own when you can otherwise just decline  

e.g.

This is what that would look like against the KG!

an exception would be against the Danish

This is how I would fight the Budapest!