If you do not know that, why are you even fitting aids??
Hearing aid performance is not perfect and the results for the user are very subjective. Of course, if you are a conscientious professional, you already know that and your question is just flame-bait.
Are you saying I should have kept one of the sets of Phonak aids I tried last year? I do not think that AuD. could program them satisfactorily if her life depended on it! I could maybe see charngin for custom ear molds, but this person did not, probably because they were not sure whether state law would permit that. I went to them looking to replace my 7 year old aids, not as a trial.
I am now reasonably happy with a different brand of aids from a HIS who calls for help if he thinks it is needed.
You know cellular phones have a mandated no-cost trial too, because of the variability of experience.
If you have an issue with the law, please find a different profession!