Okay, here's my $0.02.
There are always going to be 'problem' clients - ones that don't want to comply, that complain about the cost, that read on the internet and then try to sound like they know everything about it as a result, and those that are just plain rude. Now, if you look at the total percentage of 'problem' clients, it would be what, 5%? Something like that?
Now, how many of the clinic's clients are 'professionals' (RNs, EMTs, MDs, DOs, DDSs, etc.)? Maybe 8%? Ish?
So, how many of the 8% are also part of the 5%?
The reason we notice these people so much more is because, when they are both a 'professional' AND a 'problem' client, they have a bit more background to toss around. They think that this background means that they are able to handle a lot more than they actually can, or that they are giving good input...
So it's not all 'professionals' are 'problem' clients. It's just extra difficult when they are.