Buying a used CPU

I'm considering a build from scratch just to have a backup desktop. If I buy a used cpu what are the risks, and if I buy one how can I check it to make sure it isn't damaged? What questions might I ask the seller to avoid buy something that has been abused?

 

I would ask the seller the following questions:
1. How long has the CPU been used?
2. Has it had its heat-sink changed at any point in time or is it stock?
3. Has it ever been overclocked, how did that go, i.e. for how long was it overclocked, did it ever crash or show signs of instability.

I would check the CPU pins - whether they are all vertical and none are bended or something.

 

Look at the seller's feedback on whatever references they use (eBay, Heatware). While not foolproof, it's a very good indicator of how well they treat others in a deal.

 

Thanks for your help, but I've decided to buy new.

 

honestly electronics work or they don't. There really isn't a foolproof way of avoiding failure without paying retail.