I am in process of finalizing the deal for sapphire GPU but the buyer have a hand written invoice so i would like to know if i will be eligible to claim warranty in future also where is the service center in lucknow
Take it to them, get them to write the serial no. down, clearly, now put a stamp on it and sign below it.
Don't go for it, that bill is sketchy at best. Get the serial number noted, it could be rma'd as well.
Good, why don't you get 7870 @ 16k? Its as fast as 580 and has 2GB RAM?