I'm not a greeter but if I were, I would not purposely play blunders but I also would not try to crush a new member either. I would merely play a fun, relaxing game. Of course, when I was a new member and was playing a greeter, I did what I could to win, which is something that I do most every game I play.
I also believe that most anyone could sign on to be a greeter and that if a low-rated player is playing you then maybe he or she is making the blunders because he or she is still learning.
One thing that I found to be very frustrating with my greeter game was that he continuously used vacation time and the game dragged on and on over several months.
I started my first greeter game today, and my opponent blundered a knight on move four. This being a greeter game, I decided not to take the knight, but I let my opponent know in the chat that I could have taken it. The problem is, I'm unsure of what philosophy to adopt here.
I wonder how the rest of you play greeter games. Do you let the opponent blunder multiple times without penalty? Do you play to win at all costs? Or do you allow X blunders and then go in for the kill? :-)