I'm pretty sure I've come across those people as well. It was a while ago in BHS I was looking at the jewellery and one of them came to me and asked if I like make up and started showing me all these things they had and telling me how fantastic they were, but I told her I didn't need any more make up and managed to get away. But I remember now she handed me some "free" stuff, of course it was only "free" if you bought the other, overpriced crap.
I really try to avoid these sellers now, I was once cornered by a Dead Sea Minerals (I think that's what it's called) lady in Debenhams and she sold me some hand stuff. She lowered the price twice when I said it was too much and I still ended up paying way too much. Never again.
Forgot to say, I've ordered the new ArtDeco palette and 4 eyeshadows and the iridescent nail polish from BeautyBay, since the Guildford Debenhams didn't have it yet, plus I also ordered the new Too Faced heart blush, it's so pretty.