I have had second hand laptop, worked fine for like half a decade. Power tools, I've accumulated some of my families and there's been nothing wrong with them either. I wouldn't buy second hand clothes, sheets, beds, mattresses, couches etc.
Most of the stuff I buy is second hand or surplus... (Electronics, building supplies, tools, clothing, whatever.) Except for food... Used food is not really something you should buy. seriously!
clothing some people can wear other peoples used clothes...i will not and basically everything mentioned by Irminsul ....basically anything that can hold bugs or sex stains is out of the question oh and i dissagree about the second hand power tools...a whole lot of my tools are second hand and those are usually my favourites to use because each tool has a memory attached to it of where it came from or who gave it to me ...a lot of my tools were my fathers and/or grandfathers..some were found in salvage cars some were found on the highway some at yard sales ...i like the memories