Are you close to it or is this an online purchase?

I wouldn't do an online purchase except through the usual retailers of a used XBX because if they got it console banned for hacking it you are boned.

That model console, I have one that model as well, was prone to the overheating issue (RROD) so I would ask if it had been refurbished at any point.

Take a game that works the machine a bit such as Forza, Skyrim, Fallout3 etc. and ask to be allowed to play it for a bit until you are ok with it (30-45 minutes should be good).

Sounds like a lot of bullshit but used Xboxen run you a wide range of risks that you may have not seen before purchase.

Oh yeah, inspect the plastic work on it for any evidence of tampering or removal, usually an overlooked item that could mean it had been modified at some point, face plate is no worry you want to look at the sides and the clamshell for signs of prying.