I have been reading these letters sent out to 'rude' customers. I feel that this is a very bad area to get into, as, for myself, most of my work comes through word of mouth, and the fact that I am seen all the time in the area. I have had my share of rude and ignorant customers, but have dropped them as 'quietly' as I can.
Usually, if I am asked to do anything extra that is big, I try to leave it 'til next time, saying that I haven't really got the time now (as I have phoned several customers, and they will be expecting me at such and such time time), and I will make a note and will be able to allow the time next time. I even do this with new customers, unless it's a small job. I recently put my prices up, where-upon this woman said "what for, it's only a ladder and a bucket of water". they're just not worth bothering with, and I certainly wouldn't write letters or emails.
I was in a job once where rudeness and abuse was given regularly, and was sent on a course to deal with it. So remember this next time... The problem lies with them.