I taught Consumer Economics for years and one of my favorite days of the week was Fraud Friday. Every week I presented examples of scams and ripoffs. Basically if something "seems to good to be true" it is in all probability, NOT TRUE. Every class was taught the idea of a Ponzi Scheme(Can you say Bernie Madoff). Every class was taught the definition of a CON man. CON is short for confidence man. In Ponzi Schemes, people are conned by giving huge returns(paying people off by increasing the number of victims).
In the end you have to have your antenna out and be on the alert. But also remember that 60 percent of the service stations found nothing wrong. Second opinions were offered with honesty. And finally the key to avoiding ripoff and scams is to be a bit at least a bit of a "cynic". The key to recognizing a Ponzi Scheme is the very large returns on you money and not being blinded by the dollar signs in your eyes.
By the way, I love Consumer Reports, they take no advertising(thus cannot be pressured). This magazine will help you wade through the morass of advertising that makes it difficult to judge the TRUTH about goods and services. It can help balance your cynicism.