Pretty amazing I can sell my 1070s for over $100 and I paid $340 for them over 3 years ago.
Yeah but you need to understand gpus prices are not like used to be, gtx 1070 used to be sold for $349, now $499. Yeah, if you buy a 3070 today for $499 and then gpus prices increase once again to a 4070 $699 then yes you will have a resale value better than when you bought and that will hold but pay attention that $349 you paid in 2016 is today $499, inflation and other things. A good example is when you could buy a 3 bedroom house for 500 dollars some decades ago and today that money is worth a 3070 ehhe
If you apply inflation, the 100$ resale value is around 30-50$ when that card is still brand new years ago. That's why for people who ROI their cards many times over, they just want those old card out of their precious space, so they can put the new cards in their place.