I could recall swapping out a 4 speed in a chevy back in the 80's with a junkyard one that was suppose to come out of an another chevy with low miles. The replacement turned out to be in worse shape than the one we took out. All the bearings, and syncro's were wasted. Even some of the gears showed excessive wear. I slapped it back together, and took it back.
Ebay has been ok for me as long as you know exactly what your looking at/for. Hopefully they now claim they are more secure, but in the past I've had my credit card hacked more than once with use on eBay.