From the other comments on this thread, it seems like Steam was using a zero-confirmation payment validator of some kind. That makes bitcoin payments Steam acce

From the other comments on this thread, it seems like Steam was using a zero-confirmation payment validator of some kind. That makes bitcoin payments Steam accepted effectively a form of check, and if customers exploited this to double-spend bitcoin, then they paid steam with a hot check. Hence, fraud. Should Steam used a different form of validation? Yeah, that would have let them reject some (most? all?) of these fraudulent transactions. But anyone exploiting that situation to double-spend coins was committing fraud just as much as if they had written a worthless check, used a stolen credit card, or tried to pass off a counterfeit $100 bill.