What to Look for in a Concentrator?

[Deb L]

I have an opportunity to bid on a used concentrator at an upcoming estate auction. I will have no idea on the model, size, etc., until I get there. Could some of you experienced people give me an idea on what to look for/at so I can make a somewhat ;) intelligent decision and bid?

Hopefully I will be able to plug it in but having never used one I don't even know what to check if I CAN plug it in!

Thanks for helping a noobie out.