Are you buying or selling? If you are buying in hurry and haven't done much research, sure someone would be happy to pocket your $800. But if you are selling and you need money in hurry, you'd be lucky to get $500. With RTX2060 going for $350, the is n way I'd pay more than $250 for a used GTX1070ti. And then the other stuff is worth $125 tops, so I'd low ball you at $375.
This how markets work. And someone who is reseller would obviously try to get it for less and sell it for more and pocket the profits.