Not sure about them causing new, real issues, but I know they'll try to sell fixes for problems that don't exist. A classic is replacing filters whether they need it or not. I had a dealership 'replace' an air filter I knew was clean without asking first, and they tried to charge me for it until I asked for the old one back.
There have been news team investigations into that sort of thing, like this one: https://www.nbclosangeles.com/news/local/you-were-robbed-nbc4-i-team-exposes-new-tricks-and-tactics-at-jiffy-lube-stores/2060915/