I queried this just a couple of weeks back, as new to Golf GTI and TPS, and most responses on here said it would be ok.
I called my local branch (Poole), and received a very warm reception - no problem not being in the trade , and given a small discount. I bought GTI floor mats and a touch up paint stick, saving about £10 on VW dealer price of around £85, so was happy with that. When I went to collect, there was this massive white board, with individual staff monthly targets, and I even commented "no pressure then?", so I think they need all the business they can get. A silly head office instruction, if that is the case, or maybe you came across a 'jobsworth'.
If it were my business, I'd take the money off anyone!