Part of an Unreadable Disclaimer on many commercials that seem to be promising a lot and asking for not much in return, "results not typical" is an indication that the deal being advertised is probably not as good as it sounds. Often, you may have to do a lot more work than the ad promises, you may have to pay hidden fees, and indeed, you may just have to be lucky. As you can probably tell, this is a way of getting around truth-in-advertising laws; legitimate items with a risk attached to them, like securities, will tell you in great detail what you're getting into, and won't try to sugar-coat things too much.
Before the late 1990s, this was almost entirely specific to commercials for diet products. An ecstatic (and genuine) customer endorses the product by proudly stating "I lost 60 pounds!" What you're not told is that this particular customer was a fanatic about losing weight and pushed herself far harder than the average schlump would, thus losing twice or more what the plan or product really promises. The UK equivalent is "As part of a calorie controlled diet"; this is occasionally spoken by a reassuring female voice, but not usually. Since then, it's shown up on just about anything where the product may not work as advertised or where you may lose money, such as "make money fast" schemes involving the stock market or real estate, multi-level marketing systems, and "penny auction" websites that charge a small fee per-bid.
Disturbingly, it's even appeared in commercials for a chain of private cancer clinics. The implication is, despite the heartwarming, soft-focus testimonial from the patient other doctors had given up on, most people told they have fatal cancer will, in fact, die from it — but give us your money anyway!
A variant of this that used to appear in car ads in the US was "Your mileage may vary" (which, by the way, was the Trope Namer for our own YMMV tabs). It was downplayed in The '90s, when people stopped caring about gas mileage, but it's back now, in the fine print about which specific EPA mileage tests were used and how it might not reflect your driving habits (often with a link to fueleconomy.gov, the US EPA's repository of fuel economy information).