All over Craigslist people are panic selling their 1070 and 1080 it seems.
Some are even below what the retailers are selling them for.
Basically a 450 day ROI is scary for most.
First, dump their prices should shops due to coming soon dramatic surplus. Also it's a good time to sell your videocards right now because they are overpricing and not many people as i see understand what is going on, many still want to buy new equipment. Especially you bought this cards in the spring or fall 2017, 1.5 - 2 times chipper. If not - more tough decision. Hold the ground may be - keep mining still itis profitable. But if ETH dropped another two times there will be no buyers for equipment and mining becomes not profitable at all considering electricity costs.
But it's business, it's not fun money for nothing. If you in - you should took all risks.
For the 1080Ti at the current price, the ROI is 500 days after the electricity cost. So it is better to buy the coins directly.