I think if you do things with a little bit of knowledge and attention then there is no issue at all while using cryptocurrency. I know there are still lot of phishing attacks and keyloggers running all around but it's a truth that a little bit of attention while making transactions can save you from scam.
Using used computer parts is risky, even if you have enough knowledge and pay attention to securing the safety of your wallet, we really can't tell the if it is safe unless you know the seller, you can assure that he won't fool you when it comes to the parts of the computer. But of course, it's better to buy new parts even if it's cheap, just to secure your own safety.