Mastering French Manners, the hard way

Thank you, I loved it. I know all about etiquette in the states and now a bit about France but what is the etiquette here? I have yet to find a resource.
"I picked up a skirt to try on, and as I took it to the
changing room, the shop assistant shouted out across the crowded room:
"I wouldn't bother if I were you - it'll never fit!""I know an american girl (very attractive and slim) who walked into a shop on santa fe and within 15 seconds the girl working there said, "we have nothing in your size". Now that's customer service...
Don't feel badly! I'm 5'11, so when I walk into most places, they tell me they don't have my size. I sometimes wish I was short and fat, because a lot of places seem to have very large sizes, but they aren't long enough. Short friends of mine have said the same thing.