Un-classy chassis. If someone says your chassis needs lubing, check it out before doing anything. Most cars built in the last couple of decades don't require lubrication. And if the mechanic says he can put in a fitting so the chassis can be lubed (pumped full of grease), don't fall for it. Adding grease where none is required could lead to problems.
Looney tune-ups. Computer-controlled engines have made the standard tune-up a thing of the past. It used to be a tune-up called for new spark plugs and ignition parts such as a distributor cap, points and rotor. Aside from spark plugs, cars don't have points and rotors, and many don't have traditional distributor caps.
Filter fantasy. There are a plethora of filters -- oil, air, fuel, transmission -- on modern vehicles, and they all need replacing at some time or another. But not at every oil-change interval. Air filters often can be blown clean with compressed air and then replaced at every other oil change. Check the owner's manual for recommended replacement intervals for all filters.
Transmission-friction fiction. Flushing the automatic transmission system also is often recommended by service centers as a routine maintenance item. But most manufacturers say it's not needed until at least 60,000 miles -- if then. If your transmission has a filter, check the owner's manual for when it should be replaced.
Hot flushes. It used to be conventional wisdom that you drained your radiator twice a year at spring and fall. But most cars now have closed systems that don't lose coolant over time, and modern coolant fluids -- antifreeze in our parents' jargon -- can last two years and more before losing effectiveness.
Injection deception. Sometimes cleaning fuel injectors means adding a bottle of fluid to the gas tank; other times it's a mechanical procedure involving a sort of pressure cleaning and chemical wash, and it can be pricey. Either way, don't do it unless called for by the manufacturer. Few of them do. Gasoline is required to have a certain detergent component that will keep injectors and combustion chambers clean. If your vehicle is running rough, there are likely other causes and injector cleaning isn't likely to help over the long term.
Warranty validity. Some dealers will tell you that you have to get the recommended service items done at their shop to keep your warranty in force. They may even tell you that you have to follow their supplemental service list. Not true. You can get service done anywhere; you can even do it yourself. Just keep records and receipts, should any questions arise over a warranty claim. What is true, however, is that doing no maintenance -- oil changes and filters at recommended intervals -- can void a warranty.