He said he doesnt want to pay $300 not that the 40gb cost $300..anyways Ive bought refurbished systems from them before,just know a lot of people dump there consoles because they A: need money or B: somethings wrong with the system so its basically a crap shoot whether or not the system is in good condition.
As for the return policy im sure its changed since ive bought a refurb,but you should be able to take the console back into Gamestop (everything that comes with it,even the box) and exchange it.
Also ask if you can test it out before you buy the console,best way to know if somethings wrong or not