Not all plumbers are created equal and some states allow anyone to buy a so called master plumbers license.
For example to become a plumber in many areas there is no practical testing just a bare minimum stand knowledge of a Mickey mouse code (if any).
Some of the better counties require the following
1- A five (5) year apprenticeship consisting of 10,000 hours of OJT and 744 hours of class room studies
2- Having proven that they have ten (10) years working in the field under the direct auspices of a LMP then they are eligible to take the 4 part plumbing exams (total testing time 16 hrs)
3- Require the LMP to take continuing CEU's and know why certain materials should not be used as cost is not the only factor that should dictate usage.
To many localities cater to the mind set of the tract house builders who try to get in and get out as fast as possible using any materials that help get a speedy job accomplished and forget the environment and let the next generation worry about the toxicity that they installed.
Much like the government knew in the late 1800's about the effects of black lung (coal dust) and asbestos (See the white lung association) they(government) looked the other way as life was cheap and the name of the game hooray for me and screw the next guy.
PVC is very toxic make no mistake about it and many installers never take the proper precautions on the installations.
Today with lawyers running the country and no one takes personal responsibility for their actions there is going to be a whole new generation of "victims" who came into contact with plastic poison and bacteria that was incubating in the water heaters as the temperature was turned down so low (125 deg F) that bacteria is no longer killed as it was when the temperature was above 140.
Unfortunately many contractors fall into the get the job as cheap as possible mode and could careless about the quality of life issues and the future of the environment.
With gas prices sky rocketing the price of plastic is not cheap any more and why would anyone settle for a second rate job if given the options and were told of the various materials available?
One cannot rely on code officials to protect them as history has shown "codes" did call for asbestos for fire proofing even knowing the dangers involved.
A real master plumber looks to protect the health of the nation not look for bottom of the line piping systems.
This has nothing to do with profit it has to do with common decency.
I think any so called plumber who would stoop so low to install an AAV should have their heads examined as why would anyone knowing the effects of "sewer gas" want to take a risk of exposing building inhabitants to all kinds of dreaded diseases?