Fuel Injector Service

Unless there is some problem or symptom, it sounds like they need the work to stay busy.

They may be basing their recommendations on mileage. Keep in mind that even the cheapest gas today has all kinds of detergents and additives. So other services are usually not needed. Spark plugs today commonly last 100,000 miles. If there's excessive misfires, the Engine Computer will detect them, set the appropriate diagnostic fault code to indicate which cylinder is responsible, and turn on the Check Engine light to tell you.