You're dreaming if you think you can sell a seven year old H20 for $100. I've acquired a few over the last couple years (for my commercial account, where the tuner matters to me and the lack of DECA and updated software/HD interface do not) and the price has ranged from free (given by a friend) to one I bought on Ebay for 99 cents (plus $30 "shipping") for an owned H20-100 - I wouldn't take an H20-600 if you offered it to me for free.
Maybe some auctions appear to go for high prices, but I'll bet it is shill bidding. There are buy it now auctions for owned H24s on Ebay for well under $100 (many bidding auctions would undoubtedly go for even less) and AM21s cost about $50 to own if you require the OTA tuner. Why would anyone pay anything like $100 for a seven year old H20, versus a much newer H24 that has DECA built in, ethernet built in, has the HD interface that is still getting regularly updated, etc.
Looking at Ebay there have been recent auctions for H20s won for 99 cents, even for those claiming to be owned units. You can set a reserve price of $50 or even $100 when you try to sell yours, but you have to find the sucker willing to make a bid that high when there are other H20s selling for much less, and much newer and more capable receivers selling for a similar price range.