In shop fuel injection service is also called a "3-step" because many shops use the same system.
A special kit is used and that is where about half of the purchase price for the service goes.
The kit has three containers in it. One is added to the tank, and the engine is started and allowed to idle for a while. The contents of this container clean out the fuel pump, fuel tank, lines, and do some preliminary cleaning of the injectors.
While the engine is idling, the tech prepares the second step. The second container from the kit is a superconcentrated fuel injector cleaner mixed with an equivalent of gasoline. This is poured into a special flushing cylinder. Shop air is hooked up to this cylinder which pressurizes the contents. The tech stops the motor, disables the fuel pump, and removes the prime from the fuel system. Then the tech hooks up the flushing cylinder to the fuel injection system either by way of the test port or by unhooking the fuel lines and hooking the cylinder in there. Then the tech starts to motor. The mixture in the flush cylinder is capable of running the engine. This cleans the injectors.
Finally, after the flushing chemical cylinder runs empty, the fuel system is hooked back up, and the fuel pump is turned back on. Then the air induction system (the ductwork from the air source/air box/filter to the throttle body) is removed and cleaned with the spray in the third container. Then the throttle body is cleaned out with the same spray. This is the third step.
Everything's put back together and the car is shipped (given to the customer.)
I beleive we charge more than $90 for this service where I work.
Unless your engine is idling rough, misfiring, or lacking power, I would decline the service. When you come in for your oil change, most service departments will check the entire car over (fluids, filters, brakes, tires, exhaust, suspension, check engine light, etc.). A good mechanic can do a full inspection with a LOF (lube, oil, and filter) that will turn up any work the vehicle needs in 30 minutes or less. This is standard practice and it's a combination of looking for work (money to be made) and CYA, which is short for cover your @$$.
As I said, unless you are having problems, decline the serivce. This service was most likely suggested to you because the tech found nothing else, or because the maintenance schedule the service department has access to told them to suggest it. So, unless the vehicle is under some sort of warranty you wish to maintain that requires you do this scheduled service, you likely don't need it at 43K miles.