I doubt many pawn shops will have an compressed air for you to try it on. Front bearing play, trigger integrity and forwards/reverse buttton is about all you can see. They are easy to take apart, but I expect that will be too late. The vanes do wear, but well known brands are replaceable. Mine are still servicable after more than 20 years. The rotors do get scored but it has to be really bad to affect anything. Having an inline oiler and filter really helps. I would have a good look on ebay or any machine sellers and see what sort of prices are being asked - mine was not expensive brand new and this applies to most air tools - then you can see if something with a guarantee is better or worse value than what you find. I should have mentioned, check out the output of your compressor and the air consumption of your proposed gun. NFG if you only have a little pancake thing. I only ever used mine in workshops, so consumption was never an issue for me.