This is how I look at it.
You can quit WHENEVER THE HELL YOU WANT!!!!!!!!!!!!!!!!!
I had a situation come up like this before when I was playing someone @ Q-stick cafe in Holland, MI.
A guy wanted to play some 20$ sets. And from the get go, I told him I really didnt want to play, wasnt in the mood, bla bla bla, but ended up playing anyways. And Neil knows the guy, whom I will only refer to as Paul. Well I win the first set, and notice he is just banging the balls around, kinda half-azz shooting.
Well I win the next set, again, he is doing the same crap. Well after I win the third, I said I was done. Well of course, he blows up, saying I cant win, untill he says so. I was like thats BS, i can quit whenever i feel like it. And said, so am I just suppost to play till, i get back to even or in the hole?
Needless to say, he refused to pay up, And I will never ever play him again. And this may should low, but I also warn certain guys, about playing him and that he should call to post up the money before hand.
Also, this is something to think about too. If you goto a casino, and lay down 10g's playing blackjack and hit 21, do you play till you get back to even or, take your money and run???