As some will know we sell a lot of used chainsaws on Ebay near all of which we know where they have come from. Our policy is to tell the truth and stand by what we sell, the last thing we want are complaining customers.
What needs to be remembered about buying on Ebay is that there are 2 types of seller, business and private. Business is defined as someone who sells items to earn a profit but the problem is that a lot of small traders hide under the mask of a private seller. If you buy off a business seller the law protects you from buying a dud in that you are covered by the Distance selling regulations. If for whatever reason you are unhappy with your purchase the you have 7 working days to advise the seller that you wish to return it and the worse loss you will have is the carriage charges. If you drove to see it then you can quite often rack that cost up in fuel and time. If you buy off a private seller you have very little comeback and will be a private legal matter.
It is well known that Stihl and others have clamped down on online sales so us registered dealers will not distance mail order sell and hence any new Stihl saws that appear on Ebay could well have a nasty history apart from the odd genuine insurance replacement being sold by the private seller.
As for buying used from a private seller, in my experience, apart from a few genuine cases, any small to medium user only cashes his saw in when its past its best. As seen in many adverts "only used a couple of times" on a Stihl saw, well we sell hundreds of new saws in a year and in my experience once a customer buys a new saw, he tries to hold onto it and generally only parts with when his shed is broken into or its life expired.
To sum it up, there is the odd bargain about but ask yourself why its for sale and who is selling it. Best idea is stick to a trusted source, be it a new or used saw.