We process CCs for no additional cost as well, and we're much more streamlined than they are. We use a drop-down menu for Comes With rather than making people type it out. The people who sell games for a living love us because of how streamlined we are.
As for millions of potential buyers, sure... but most buyers start their search from Google. You'd be surprised how many people create an account to buy a $6.99 game and never come back. (Now, our retention efforts suck, but that's a different story.)
how do you protect yourself from scammers? i.e. someone using a stolen credit card to buy from themselves or someone doing a chargeback after an item is shipped.