All modern gasolines are solld with additive packages mixed in that include sufficient detergents to keep a properly maintained car’s fuel system clean and operating properly for many, many thousands of miles. In most systems they’re evn going strong after a few hundred thousand miles, although occasionally an injector will stop opening or something of that sort. An occasional bottle of injector cleaner added to the gas tank is prefereed by many to make sure, but I let the gas additives do the job.
The dealer may also be referring to an “induction system cleaning”. You have a system in your car that allows a tiny bit of exhaust gas to be reintroduced back into the engine with the airstream, and over many, many miles a small carbon deposit can build up. But If the engine is properly maintained and kept running properly I don’t believe induction cleanings are necessary either.
You do not need that a system cleaning or IMHO an induction system cleaning. The dealer simply needs to improve his revenue stream.