What is a certified check?

im selling a camera on craigslist.com and i have a buyer but he send me a email asking me for my info so he can mail me a certified check..ok heres the problem im selling the camera for 1500 and hes giving me 4000 he says as soon as i chas the check hes gonna send someone to pick up the camera ad he tells me to send the rest of the money to the shipper do u think this is a scam trying to make me cash a check for me help me out tell me what u think??? kk? thanx? xD