Look it over and make sure it works, and on the bottom center of the back of the device make sure it does not say "Demo Unit-Not for Resale." The only way to obtain one of those is to steal one. And as always: no receipt...no purchase.
Buy it as long as it is within a reasonable price range.
I bought a 16gb wifi used. Guy wanted 500. I bought for 450.
No receipt.
Guy just lost his job was moving etc.
I could have bought new for 540 which includes tax from apple but I got for 450 I did good!!!!!!