How do people who run second hand shops keep a straight face?

I was in Withernsea (near HULL - UK) at the weekend and we walked past some second hand shops (there was a lot of them, in fact every other shop looked like a rag and bone-mans yard!!). I cant believe the absolute crap that they sell (or don't sell, if the shop I went in was anything to go by). They were trying to sell second hand, DIRTY clothes that wreaked of urine, rusty cutlery etc. We even spotted a vibrator (top shelf). How do these people have the audacity?