[voyou]

"there is a HUGE financial incentive on the part of sellers"

At least up until now, there have been ad sales, which you can think of as an incredibly heath-robinson micropayment system: a small amount of what I pay for every product I buy goes to their marketing department, which passes on a smaller amount to advertising firms, which give it to websites. The viability of advertising largely removed the incentive to develop micropayment systems; hopefully that's now changing.