Maybe there’s a better place for this question, but how do you make sure a used laptop is safe? Or would removing Windows and installing Linux be enough?

I want to buy a laptop for Linux, and would buy a used one so that it’s cheaper but I have to admit I worry about it. I know one could be worried even about new laptops and what manufacturers could be up to, but I feel like the unknown arbitrariness of a used laptop gets to me.