I've worked in management, dealt with the public, and now own my own company. I don't accept rude treatment by salestaff.
Here's what I like to do:
Remember that a great number of stores hire secret shoppers. If I encounter treatment like the first poster, I go up to the salesperson and make a point of noting their name (or asking for it, if they're not wearing a name tag). If they refuse to give it, mutter something to youself like "...refused to give name..." as though you're making a mental note. Then ask if he/she happens to have the EXACT time. Even better is if you happen to have a PDA or piece of paper with you, walk away from the desk a bit and write down the name, time, and description of the salesperson. It should be enough to get them wondering if they're about to be written up.
If you're still ticked about the treatment when you get home, write to the company and let them know! You've now got the information to give them so they know precisely what store and who the salesperson was. Be sure to write the letter with a clear, objective tone. Don't say "Your sales person was mean", give examples. "I was in your store today (washington mall location, my city) and received extremely poor service from one member of your sales staff (Sally). Sally refused to assist me with finding items, she was rude and curt in her responses to me, and proceded to make derogatory comments about my attire to other members of your sales team. Needless to say I am shocked at the treatment I received at your store, and will not be returning."
In situations like the car salesman that wouldn't let the poster test drive the car without her husband, it's times like that when I ask for the manager. Again, keep a calm and reasonable tone - no one gives any credibility to an irate, hysterical person. Make your complaint, find out if it's company policy, and then say "I'm upset and unhappy at being treated this way, and I'd like to know what you're going to do about it."
Being an overweight person myself (less so than I was, but still overweight) I've also encountered the rude and persnickety sales person who feels I don't have a right to shop in the smaller sizes. I also had one who told me that there was nothing in the department that would fit me, and I said "What makes you think I'm shopping for myself? How do you know I'm not buying a gift for someone else?" And frankly I don't see it as any of their business if I'm buying something in a smaller size or not. I purchased plenty of things that were too small when I bought them, and are now too big on me.
sales people. When she works an 'open house' she gives time and attention to everyone. When I asked her about it (it's how we met actually). She said you'd be surprised how many people 'wear' their money and those who look like they've got plenty sometimes can't qualify for a home loan!
) But I also don't expect to get attitude from someone whose job it is to assist me.
I could never actually shop in heels and a dress. 
So don't automatically assume fat people can't shop there. 
