Buying Iphone off of Craigslist, what should i know.?

I am buying a 2g 8gb unlockediphone from somebody from craigslist. What are all the things i need to know about saving stuff, such as saving a new email and password. Also if i reset the iphone so that my email and password can be saved then will it need to be unlocked again.

Basically i want to know all the stuff i should do when i buy a used iphone off of craigslist. Thanks