(If pharma companies can deduce which brands are prescribed by which doctors, then perhaps there lies a problem we can easily solve.)
How about buying technology? You've never been treated to lunch or drinks or something by a vendor? "You aren't buying a product, we are forming a relationship, you'll be a partner in the future of <widget>". Did you guys buy it?
Most doctors are reasonably intelligent on paper, they all have advanced degrees and all their friends think and tell them they are smart... But why would the ratio of great to bad be different than in tech? I'd think that you could "hide" more easily in medicine, there are all sorts of ways to make a big pay check without doctoring, like selling medical marijuana cards or simply selling prescriptions for big pharma, people will actually come in and ask for certain drugs because they saw an ad. Fact is, most sicknesses are defeated by your immune system, not some pills. Cultivate the right practice and they can simply be legal drug dealers, get paid and their customers will be happy. And nobody wants to think their doctor is bad, but before anything substantial or chronic treatment (like you need this drug forever) you should always seek some additional opinions.