Speaking from the other side as a business owner (not mass-market retail, but the issues are all the same really):
1) some customers are simply impossible to satisfy; they do not fit your business approach but haven't realised it yet. The solution is to identify them rapidly and subtly/politely disengage from them and decline their custom before the problems arise. Preferably by referring them to a competitor so they can go hassle them instead. Alternatively, simply lie back and take it... and think of the money while doing so.
This made me smile. When I was in college, I went to work on the sales floor of our family furniture store. Keep in mind the place was called
Affordable Furniture, we didn't carry junk, but it wasn't high end either. One evening an older, well dressed lady came n. IIRC she was looking for a sofa. After about 20 minutes of her nitpicking the most minor of flaws on just about everything in our inventory, I was beggining to wonder if there was anything I could do or find to make her happy. Being young, I wasn't sure how to handle the situation so I told her I needed to check on something and would be right back. I went behind the counter and told my father what was going on and asked him how I should handle it. He just said watch and learn.
He walked over to the lady, introduced himself as the owner, thanked her for giving us a look, then noted that she appeared to be a woman of good taste and high quality standards. He then informed her that our clientel were primarily middle class families in need of good, but affordable furniture, thus the name. With that, he informed her that we would have nothing here that would interest her, and that a woman such her would only be served by shopping at one of the two high end/high priced stores in town. All the while he was walking her towards the door. He thanked her again for coming in and left her at the door with a somewhat bewildered look on her face.
When he came back to the counter I told him I was confused. Why didn't we try to make a sale? He said something I've never forgotten. He said no matter what you do, how hard you try, how far over the top you are willing to go, there are some people out there that just cannot be pleased. They are only happy when they are making someone else miserable. They live to bitch. He could tell right away that was the type of person that she was and he would much rather watch the sale walk, than have to deal with the headache for months to come. Let her spend three times the money somewhere else and be up their ass.
He then went on to point out that the entire time he spoke with her, it was in a pleasant tone, and he had a smile on his face. While turning down her business, he was never offensive, instead almost complimentary. He told me the point wasn't to piss her off, just to get her to shop somewhere else. I then asked him how he got so good at dealing with nitpicky, bitchy people. He smiled and said, "I've been dealling with your grandmother for over 20 years, haven't I?" I kid you not, true story.