The recent 'crypto crash' may have resulted in a large-scale dumping of slightly older cards onto sites like eBay. Consequently, this may drive down the prices others with the same GPUs (e.g. gamers) can ask for their listings. In addition, this is the season to grab cash for upgrades.
https://www.notebookcheck.net/Crypto-crash-may-have-led-to-deluge-of-second-hand-GTX-1070s-onto-online-markets.366081.0.html