UI Layout (and market woes)

I've got the majority of the hand-drawn UI layouts uploaded to Basecamp. The usability seems pretty simple - speed is the key. The good news is that if we need to switch markets for some reason, it could be done rather easily. Depending on the market, the categorization system would need to be modified.

I'm not going to lie - I'm still somewhat worried about the market. Why would a user post a wanted ad when they can just as easily go to eBay and find the item there? Even while asking that question, there are millions of wanted ads posted each year on other non-exclusive sites. I know the market is there - I just don't understand it. Here are a few reasons why a buyer might want to post a wanted ad:

1. Item customized exactly to the buyers wants
2. A "set it and forget it" mentality - don't worry about someone outbidding you
3. Sellers bidding to give you the lowest price

Here are some reasons why a seller would enjoy wanted ads (no question there):

1. Ability to immediately find people interested in your item (perhaps even automatically)
   
2. Ability to undercut the competition
3. Cost per acquisition - no sale means no cost