>>no, politician shoud be allowed, but should make his investments public knowledge, same as the doctor ordering further tests in centers he owns part of.

In a US context: it's actually illegal to refer to your own testing/service facility unless it's in the same premise as your practice, in which case the convenience and immediate access by the physician best placed to interpret the results, is said to prevail. There's lots of conflict about this, with some specialist bodies calling for this also to be outlawed and others, such as cardiologists, talking up the benefits of having the cardiologist right there to interpret findings. Looking elsewhere it's common for pharmacies and labs to congregate close to medical practices which does imply that patients also like the proximity.

The question then is whether orders from your own facility are padded to increase revenue. Not easy to assert in the US when over-testing is perceived as quality by many patients and failing to do a test for a 1 in a million risk can result in a law suit.

As for prescribing meds, lets be real: unlike a politician whose decision can involve tens or hundreds of millions of dollars one way or another, the notional physician prescribing expensive drugs from his own company is a minnow even if s/he does it for every patient = 20 times a day. Straining at gnats and swallowing camels etc. Choosing $10,000 prostheses from your own company is more likely to raise eyebrows but if cost and outcome is comparable, where is the victim?