Smart business owners understand that customer service is part of marketing--and that no amount of (expensive) marketing will undo bad customer service. This is something I talka bout in many of my books, including the most recent, Guerrilla Marketing to Heal the World.
I have boycotted a number of businesses that treated me shabbily--including a movie theater that sold my 12-year-old self an adult ticket and made me sit in the children's section. I have not been back in the 47 years since. But the worst was our local Toyota dealership. We had a long and extended bad interaction with them that culminated in a phone call, "you have 24 hours to get your car out of our lot--and by the way, the engine is in pieces in the trunk." Not only did I write a five-page complaint letter with full documentation to the VP of customer relations for Toyota USA (which gave a too-little-too-late form-letter make-good offer a year later), not only did I never buy as much as a tube of touchup paint from that dealer for the rest of their career and was not sorry when they closed--but the next time I went car shopping, I didn't even seriously consider Toyota and bought a competing brand. That was the first time I bought a car not built or designed by Toyota since 1981--they threw away decades of strong brand loyalty.