Just to share my thoughts with regards to items marked SAS, PARA'S RM etc or "issued to blah blah" and special forces. As an ex service member of recent times (80's through to 2000) a lot of kit marked with such tag words are nothing of the sort! As others have said, before you hit that "confirm bid" button, have a quick look down your local surplus stores for a comparison. Almost every British Army item should have an NSN (NATO Stock Number) on it, if it ain't then it probably is a copy. Also on hardware, (mess tins etc) look for the "Crowsfoot" mark, again a sign of a genuine article.
Some of the kit advertised is very decent and usuable, but just wonder if it is genuine before buying - there is a difference. In my experience the majority of a Regiment soldier's kit is either "Proffed" (long term borrowed) particularly from the USA SF or put together from a mixture of sources.
Another good place to look to compare is Silvermans.
Having said all of the above, there are genuine issue kit from e-bayers, you just got to know what to look for, perhaps ask a squaddie?