I occasionally say something in Spanish that is perfectly polite in English, and the other person seems to respond negatively to. For example, this took place via messages online on a site for selling clothes (translated in English):
Me: What kind of fabric is this dress made of?
Saleswoman: Cotton with stretch.
Me: Are you certain it is cotton instead of a polyester blend? (Super hot here and polyester is the worst for the heat)
Saleswoman: Look! I don't know, it's not here with me right now!! But okay, tomorrow I will check it!!!
My question is, are there any phrases or ways of speaking that come off as rude or offensive in Spanish? Anything you should never ask about or any common impolite mistakes people make?