In Russia, the seller asks for $ 540 for a used Vega 56 video card produced in 2017.
This is the first problem. And the second problem is that these video cards were bought mainly by miners.
Gamers passed by these graphics cards.
Therefore, I prefer not to buy these graphics cards.
No no no, don't get it wrong, you can do research on your own using google, RX vega 56 is indeed very good for mining Ethereum, it can produce up to 52megahash per second, presently you can get one at 460$ on ebay, I believe that's still a fair price, it's not about been old or not, it's about profit making
I think you've mistaken RX5700XT with Vega 56 mining hashrate, only RX5700XT can do 54megahash and VEGa 56 can only do 32-34 megahash, check your calculator once again, Vega 56 isn't that good for Ethereum but better with Monero, the image below is for RX vega 56