I bought a 1990 K75S from them in 1999. Two owners, full history, very cheap. Basically it cost the same as one Bikerama had that had 9 previous owners, no history, and the wrong paint.
The bike I bought was ( I asssume) stolen recovered because the steering lock had been broken. But both keys were supplied and matched the original invoice.
I felt I was treated fairly by the guys at RS. It wasn't a brilliant bike, (althought it looked immaculate) and it wasn't necessarily a better a purchase than a much nicer one from a main dealer would have been in the long run as I had to replace the disks, rear shock, clutch etc within the first couple of months (bit like my brand new R1150GS then

). But at the time I had £2,200 to spend, and a similar mileage/spec/age bike at my local dealer was up for £3999.
RS didn't volunteer much, but they didn't strip the panniers, tool kit nor remove the note in the service history suggesting that the previous owner had allowed it to run low on oil at some point.
This was my experience. And if I ever end up working for the NHS again I would consider buying from them again. This is not to say that I would recommend them in any way shape or form to anyone else.
And bear in mind that my previous purchases had been much cheaper and from far morepotentially dodgy sources. Like West Yorkshire Constabulary......