i read somewhere that engineering samples are illegal to sell or just not meant to be sold so you might wanna ask the guy you bought it off where he got it from. i could be wrong though. it probably wont overclock well even if its multi unlocked, ES-cpu's are the pre-retail release ones and are meant for testing purposes only, like for review sites so reviews are out on the release day of the cpu, and for motherboard manufacturers so bios'es are out before the release of the cpu.
edit: looking at that guys auctions he seems to have a lot of ES cpu's. there might be a real reason he has them, but he might be doing something illegal. ive noticed that guy has a return if it doesnt work policy (aka if the person he sells to's motherboard doesnt take ES cpu's), id try and do that asap, it seems like its not gonna work. and maybe even report it to ebay, or even directly to AMD that that guy is selling ES cpu's. theres another guy who is doing the same, on amd forums someone made a post about it. also this "other guy" is in the US and posts from birmingham, and this guy is in birmingham, possibly the same guy? this is why i dont ever buy anything off auction sites, the guy who possibly conned you and the "other guy" who has conned thousands of people need to be shutdown.