If he goes out and buys a second hand RX 470 8GB for like $75 he will make about $0.25 per day prior to electrical cost and with 10 cent power its more like a loss of $0.04. If he goes out and buys a new RTX 2060 for $350 his profit will be about $0.45 per day and with 10 cent power it will be like $0.14 profit.
So which one makes more sense? I haven't really looked into the 2nd hand price for the RTX 2060 but I am assuming it won't be too far off from the new price since its still a fairly new GPU. Even with free electricity he is better off just gettin the RX 470.
Unless the alt coin market bounces back there really isn't much out there to mine profitably anymore.
Nvidia cards can be easily resell compared to rx470 which is old version of AMD card you can resell them for much cheaper than Nvidia and there are many gamers looking for RTX series. You can resell them after you mine after a few months at a good price and Nvidia cards support many algo than AMD cards. That's my best than buying a 2nd had which we don't know the lifespan of the card it might be bought last 2016 if you bought a 2nd just release 2016 then there is a chance that the card might die soon.
They do sell easier however they do still depreciate. They typically depreciate when Nvidia releases a new model.
If he bought the RX he can probably resell it a year later for a small loss, if he bought an Nvidia card he would sell it at a much higher loss in dollar terms. And just because the card was built in 2016 doesn't mean that it will die soon. The warranty is 3 years but its not the lifespan of the GPUs.
Usually what fails first on the GPU is typically the fans and there are many aftermarket cooler and many OEM fans you can buy right off eBay. Generally even if it was mined with, it was most likely undervolted and not put through alot of torture like most gamers put their GPUs through in a badly cooled computer case.