If you have free electricity, then I would not sell a video card either
Video card values have declined much faster than the profit they make at free power. Capital loss is the real risk here, not operating loss. That is why I have sold half my rigs in the hopes of buying them back cheaper later on.
But a graphics card can't be worth $0 like a cryptocurrency. Even the RX 580 8 GB graphics card can play many modern games and its price will not fall below $100 if it is in good condition. Even if it is cheaper, then what price will the RX 550 2GB have? RX 560 4gb? RX 570 4gb