Yes, how do you deal with the (hundreds, thousands, millions) of annoyed customers per day who were promised one thing but wound up paying for another?

This can't be a minor problem, either. At any given time the percentage of your users who are being ripped off by some nasty scam will be between 10% and 90%. You'll have to be very careful about policing things, otherwise the first mention of your business in the media will be "gumroad enables porn bait-and-switch scammers".