^^Yeah I think the key thing is different people will have different priorities. The way I look at it, if you have a card worth a fortune and choose not to sell it, that's not really that dissimilar from not having such a card and choosing to buy one for a fortune, as in both cases you end up with the card, but are £xxxx worse off in terms of cash. I wouldn't pay £1445 for a RTX 3080, so conversely if I had one I could sell for that price, I probably would unless I really didn't have anything remotely feasible to replace it with. I'm on a 1070ti and the prices aren't crazy enough on those to warrant selling it, but I would if they were paying over £500. Promote the RX480 from my son's PC and give him a 7950, job's a good'un.
That said, I guess a key difference from 'normal times' is there isn't really much alternative in terms of buying a card at 80% of the performance for half the price like you might normally see. It's not only top end cards that are expensive / hard to source but even midrange has suffered the same fate.
This CEX situation is a bit unprecedented in that there is a reliable mainstream buyer offering hundreds above MRSP. Effectively it's a massive incentive for scalpers as there's guaranteed profits to be made, basically any FE cards will sell instantly because you just buy up as many as you can and don't even take them out of the box, straight down CEX it goes, you haven't got to take a risk on selling to joe public to make money.