Don't rely on your garage to tell you what needs to be done to your car. Though they should know better, they may recommend a more accelerated service schedule than required by the manufacturer. Rely on your owner's manual.
Here are a few services that can be a poor use of money:
Fall and spring tune-ups
Today's cars typically need a fluid change but no tuning. Many items that used to change routinely, such as spark plugs and wires, rarely need replacement.
Air filter changes
Some garages will suggest new ones every other oil change. These filters typically cost $40 to $60 each plus labor to replace, and should be replaced as per your owner's manual
Free brake inspections
While an inspection may be fine, it's rare that when you have a free inspection that they don't find something to suggest, even if you don't really need it (or its not broken, or its not recommended for replacement at this time in your Owner's Manualů). Some mechanics habitually suggest new rotors and brake calipers, long before your vehicle really needs them.
Specials that aren't so special
Often a "special" service for (say) $100 can take only 15-20 minutes, so you're paying $300 to $400 an hour instead of a regular mechanic's rate. Even an otherwise legitimate $14.95 oil change, gives the garage on opportunity for an add-on profit by suggesting unneeded repairs. Watch for garages that always advertise "loss leaders."
While this can extend the life of your car (especially if the winter roads in your area are treated with salt), car dealers charge a premium price for this service, and don't necessarily do a better job than a reputable specialist.