I have been to precisely 2 in my life - Once to sell off some of my vast library ( seriously, a collection of around 1500 textbooks, non-fiction, lots of sci-fi and crime fiction etc) - So i selected a fair number to sell, managed to sell a fair few and made around £200 for a morning sitting about selling stuff :)
Only other time was in France and the girl I was with ws dying to check out antiques- I think we ended up with some ratty looking lampshade that she was convinced was Lalique - only it wasn't :)