What Should I Do About a GPU Hitting 105°C after Selling It?

I wouldn't offer a refund on a component that was working fine when you sold it. There's no way to know if the buyer has messed with it after the sale, like poorly reapplying thermal paste, or if they're just having buyer's remorse. Once they took the GPU, your obligation is pretty much done, especially since most second-hand buyers should've tested it beforehand.

If it’s a 3090, those GPUs are known for high hotspot temps due to their design. If it’s not a 3090, then that's more concerning. Either way, let the buyer know that you're not responsible for diagnosing issues after the sale.

You're not obligated to refund as long as the GPU functions properly, which it should. If it’s an issue for the buyer, they can always try re-pasting the thermal paste themselves.

What model GPU is it? A hotspot temp of 105°C is high, but depending on the age of the GPU and whether the thermal paste is worn out, it might not be uncommon. Also, consider if their case has enough ventilation or if they're using the PC in a hot environment. If the GPU is older, it probably just needs a bit of maintenance with new paste.

105°C is on the higher end but not abnormal. If it's an older GPU, it's likely that it just needs new thermal paste. You can explain that to the buyer and suggest they try replacing it before jumping to any refunds.