I taught for several years in an audiology doctoral program (the Au.D. is audiology's equivalent of the O.D. for optometry).  My specialty was hearing aids.  My students learned more about hearing aids in their first 3 months of graduate study than is required of licensed dispensers, and they still had 3-1/2 years of study left, including 2000 clock hours of patient contact and two more classes on amplification.  

Before Illinois closed the requirement for dual licensure for audiologists as hearing aid dispensers in 2003, I had to take the hearing aid dispensing examination.  I was dismayed at that time to see what little depth of knowledge was required, and found the exam to be overly simplified wherein it penalized the greater knowledge base of an academically trained audiologist.  Many of my peers in other dual licensure states have noted the same, and the general report across the US in dual states is that the "fail rate" reported for audiologists on dispensing exams is likely due to exactly that problem.  That is, instead of answering a simple, "it's broken," an audiologist is likely to respond, "given this model of instrument, the gain should be at least 45 decibels but this cursory exam sounds in the neighborhood of 10 decibels, so the instrument is weak internally - possibly from a bad receiver - and should be sent for repair".  Believe it or not, that second answer has been counted as wrong, even though it is factually correct.  

Audiologists - by nature of their academic credential and subsequent state licensure in our profession - are already qualified to dispense hearing aids without any further licensure being necessary.  Illinois has solved the financial aspect by having our license fees remain the same as they would be in dual license, with the additional sum being routed to the hearing aid licensure board.  In this way, regulation of the hearing instrument consumer protection acts remains funded, without unnecessary and overburdensome legislative restriction of the practice of a profession.