Pete:
As my wife would say, "That sounds good on paper."
But in truth, unless you know the people you are posting with, here's what's going to happen:
1) Someone will want to know why so-and-so's stuff is listed before theirs, or closer to the top of the page, or whatever.
2) Why do they have to pay $xx.xx when so-and-so has more items listed and is only paying $xx.xx?
3) You have no control over marketing your website, which also leads to "I'm not paying to advertise product x unless she pays to help me market mine!"
4) You probably have to pay a commission percentage for every sale to the owner, and can probably not control how customers pay.
5) The site owner will have the credit card merchant account, not you, which means they pay you when they want to. you're not getting your deposit next day like you would if you had your own merchant account. Unless they are very sophisticated, its not likely that they will be able to process payments through multiple payment gateways for multiple merchant accounts.
6) Your own website, with hosting, shopping cart and payment gateway is less than $50 a month. Add about $20 for your own "real" merchant account or less if you decide to just use paypal.
To me, that would be a much better way to go to be able to control your own destiny.
Just my 2 cents.
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