I think I remember someone asking a similar question a while back. Personally I wouldn't be keen on ebay but I know that some DIS posters have used it without any problems.
Why not try sites like www.homeaway.com or www.lastminutevillas.net as you may be able to pick up a good deal and these are sites where owners pay good money to advertise giving you a bit more peice of mind that everything will be ok.
I haven't used it yet, but I listened to a podcast about a vacation home website that sounded interesting. If you put in the dates of your trip, it will only show places that are actually available for those dates. It looks like there are lots in Orlando.
I rented a 1 bdrm villa at OKW through a seller on Ebay. I paid $780/wk and it was SO worth it. I really checked around though and contacted the seller by phone before I bid.