How can I test a computer in a public place?

I want to buy a computer that is posted on Craigslist. The person who is selling the computer assures me that the computer works, but I am still skeptical about it. The person wants to meet in a public place, not in his house. I was thinking about asking a store owner to let me use a power outlet. What other options do I have? Should I trust him? The computer is worth $55 but it would normally cost $80. It is only the tower, it does not include a monitor.