The problem with "stock" or "mostly stock" cars is that you're never sure they weren't heavily modified before. These are an EXTREMELY popular platform to mod, and people will often revert them back to stock and sell off all their old parts to maximize their returns. They can get money from the parts (often what/more than they paid if they got used to begind with, and then the car gets a premium for being "stock").
If/when you do a pre-purchase inspection, you need to look for telltale signs, such as fresh hardware in the exhaust, or exhaust bolts that ARENT rusted closed. I'm sure others will have some other signs to look for as well.