I think there are two separate issues being discussed here:
1) Should you foot the bill for a part that is broken by the guy fixing your gun?
2) Are the prices this guy charged you reasonable?
To answer the first question I would say that No, you shouldn’t be responsible for the breakage of a part that you paid to have installed in your gun. If that guy broke it, its his responsibility to replace it. The only time I would say otherwise is in the event that someone is doing a mod or an upgrade which is difficult or delicate and has made explicitly clear to someone that there is the potential for broken parts and that in this event the doctor would not be responsible for broken parts. The client would then have the choice to A) take it to a more confident doctor or B) agree to the risk involved.
As for the second question this problem extends far beyond the realm of gun doctors. Everyone at some time or another has been over-charged for something. Typically this happens a lot with contractors. Some people complain that they were taken advantage of. For me I would have to argue that consumers should be smart. While it is illegal to fraudulently charge someone 5,000$ to fix their fluxcapacitor in their car, it is not illegal to charge someone 700$ to change their front brake pads. It may be excessive and immoral but that is the price you pay for not checking prices with other places. I have friends who are contractors and it is quite common practice to over-quote jobs which come at times when they are too busy to accept them, or require more of a commitment then desired (be it time or travel distance). These contractors are not crooks they just want to make sure that if they accept business it is in their best interest.
The real reason it causes so much uproar here is because this community is a lot smaller and closer knit so people don’t like the thought of others making money off of them.
My recommendation would be to get quotes from more then just one gun doctor and to talk to other players about whether or not prices sound fair.
Misinformation in internet forums haunts me so