Like many others here I deplore racism so the following must not be taken as such.
It's very unusual to find a white English customer who haggles.
However, it seems to be much more commonplace for someone of Asian/African origin. This doesn't make them bad. It's just more ingrained in the cultures. Unfortunately, especially when they are dealing with a sole trader, the price is more closely related to the sole trader's income so it's easier to take it personally.
Some examples: I did a couple of shops, a hotel, and a couple of houses for a family of Asian descent. I got so peed off with them trying to knock down the price, I ended up cancelling the lot. Average value a bit over £100 a month. If that sounds a bit extreme, you don't know what I went through.
Another time I did a shop for the owner. Quite a small job - £5 outside only. After a few visits I was asked to clean one of the inside windows (free). I did it for goodwill. Of course, that became part of the (free) job. Price was still OKish though so no real problem. Then I was asked to clean the inside of another window (free). Did it but this was definitely only a one off. Then the job was reduced from 2 weekly to 6 weekly so took a bit longer each time. I put up with this as I had other work very close by. The tipping point came when I was stopped from cleaning due to the Christmnas decorations ON THE INSIDE. I pointed out that the original quote was outside only anyway. So that one ended.
Did a quote for a house recently. They seemed undecided as to have regular or one off (which nearly always means a one off or cancelling after 2-3 cleans). So I gave two quotes (one off 50% higher). She asked for a one off but wanted it cheaper. I said good-bye. In fairness, at least they were honest about it.
To balance this up, I have never had an Asian or African bump me for the money, whereas plenty of white English people have (including three coppers that I'm aware of). Nor have I had the hassle of them haggling AFTER I have done the job. Also, I have a number of Asian/African customers who are delighted to pay the price and don't haggle.
So, with Asian/African customers the chance of a haggle is around 30% (though close to 100% with shopkeepers). With white English people it's maybe 1%.