To buy refurbished Mac book

Refurbished and Clearance is where you will find them.

Refurbished Macs are as good as new ones. They are revised by Apple, faulty parts are replaced with new ones and Apple sells 'em with warranty and everything. It is possible that you'll find some small marks on the case, but display, logic board, etc., it'll all be just fine, working properly and tested by Apple.

Refurbished Apple hardware generally is a good buy.

Usually third party vendors handle the sales.