My question is, where would they go? If there is competition out there, then that is something that we would certainly be interested in seeing - seeing how the competition measures up, and seeing how we can offer something better. Certainly, I don't see Ebay is being competition, since there would be no cost to an initial offering here. We want to make our B&S the best available option on the market.
You seem to be concentrating on the big, active sellers - which makes sense from your stated purpose of paying the rent and I'm sure an equitable arrangement will develop for that constituency.
The aforementioned small, occasional seller or the buyer who bought an item here and wants to resell it due to size, etc. will probably just drop out, and the B&S forum will be the worse for it.