First, i've never stiffed anyone in my life, i've done business with a few people on the forum here, and have always paid and vice versa. I'm always the one exposing stiffs.
That said, if I found out, 100% I was being hoodwinked by an individual, would I pay them up? Absolutely not...
If I funded a fake offshore book with a creditcard, lost the majority of my balance, then I found out the offshore book operated by scamming everyone and not paying a cent out, i'd issue a chargeback in an instant. The deal agreed upon was if you make money gambling they pay you, if not, you pay them. If they had no intention of paying you anything, why in the world would you pay them?
The same goes for anything else in life. If I agree to buy $20,000 worth of gold coins off a merchant and then later discover they are fakes worth less than $10, of course i'm not going to buy them even though I gave them my word I would.
These situations would never apply to me though, because anyone who does business with agents/bookies online is generally broke, and it's just two scammers trying to rip eachother off. However, there are a few exceptions i'd imagine.