Need advice on selling my bass

As far as eBay goes, buy and sell a number of small, low-priced items. You could have a dozen positive reviews in your account within a month and only spend a few bucks doing it.

As far as the bass goes, I've seen Thumb neck-throughs sell in the low thousand mark ($1000-$1400) quite regularly-occasionally less as well. It all depends on how the market is, and the market is occasionally flooded with Thumbs, although they're usually bolt-on. Look through the ads on Bassgear.com and the Harmony Central classifieds to get a feel of what people are selling their Thumb basses for. Also, do a search on eBay for completed items only of Thumbs; this will give you a fairly accurate idea of how much yours might sell for if you decide to put it on eBay. Hope that helps.