I would steer clear of ebay with companies selling "refurbed engines" you get allot of dodgy foreign companies claiming they have overhauled it when in fact they just spray the outside of the engine to make it look new, highly dodgy!! I have bought a few from GTBitz, bit expensive but you get the whole engine, ancilleries, turbo the lot and you can see its all standard and not been messed around with. Stick to the forums, UKSO, TGTT, Also ALWAYS if possible see the engine running in the car, go for a spin in it, make sure its not blowing exhaust gasses out of the top breather when you rev it (sign of broken ringlands), check for oil leaks, really common to leak on the crank seals so look on the gearbox side and the crank pulley side, check for mayo under the oil cap (HG failure) and if you have one take a compression tester with you, you want 150psi from each cylinder or more and 4 pistons to be within 10% of each other. Oh and athough obvious dont buy anything with knocking bottom end bearings! Can be an expensive repair.