It's a good time to SELL GPU's.
September 2017: I bought at MSI Duke 1080ti for $660 USD.
Today: I sold that card for $630 USD
This, after flogging it mining 24/7 for 11 months
Gamers are buying up 1080ti at the moment because 20 series is not great value.
you must be selling to idiots, or paying fees to sell on ebay.
going rate for 1080tis on reddit is $500 shipped all day.