How do I know what used TH is worth? (To est. a good price)

RV trader, NADA etc values should be taken with a grain of salt. I've seen them be WAY off in both directions. RV's, like many other things, are worth what someone will pay for them. eBay is a good barometer if you look at the ended auctions to see what they are truly bringing. I got less than book for my Weekend Warrior, but way more for my XLR.