It has been conversed about many times before. I will only buy used from an OGR Forum member. I see guys every week that get screwed to the wall very hard buying on fleabay.
If you get a nib old stock locomotive and the price is very good, go for it. I like to run an add on the Forum that I am looking for inoperative engines and get a few. Many of the people (not forum people) with bad engines would rather screw someone for a few bucks gain on fleabay. They all say it ran when they sent it.
BUY ON THE OGR FORUM AND BE SAFE.