Just out of interest I put "FCP X" in the eBay search box and came up with this lot . . .
http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR6.TRC2. A0.H0.XFinal+Cut+pro.TRS0&_nkw=Final+Cut+pro&_sacat=0
FCP X, Motion and Compressor for £10 and all "genuine eBay listings".
The sellers are telling the truth as they are indeed real (aka genuine) eBay listings but that is totally different from being genuine legal Apple products.
They are completely illegal.
The seller has either bought, stolen or been given a copy of FCP X and is selling it to as many people as he can to make a quick profit.
On the other hand, the listings for Final Cut Studio are quite possibly genuine as they are pre-2011 versions that are unlikely to work on modern computers and are only really of use to collectors of historical editing artefacts.
P.S. I have just had a good laugh reading the first advert . . . the seller informs you that he has bought loads of Macs which all happen to have the full FCP X suite of apps on them and has removed the apps to sell them to you, so everything is OK.
As Tom said, the licences for FCP X are not transferrable so you are not permitted to sell or even give away the apps.
Furthermore, if you sell a Mac containing such apps, you are legally required to delete them before passing the computer on to the buyer.
I'm still laughing at the image in my mind of this guy with a house full of latest Macs all filled with FCP X etc.