Traditionally, audiology offices undercharge dramatically for their initial consultation and testing, then provide full service for the lifetime of the device. And not just normal electronics service. Often patients will come back every week or two for months to get the fit just right or to get some coaching relearning how to hear conversations or just having the nice lady in the white coat show them how to replace a battery for the fifth time. A lot of clinics will even throw in "free" batteries for life. The cost of all that service ends up getting rolled into the initial purchase price for the hearing aids.
This is dumb. Most audiologists that I know think it's dumb, but it is the status quo. There's a move in the industry toward "unbundled" billing (i.e. charging an hourly rate for services and selling the aids at a much more standard retail markup) that I hope catches on, but it's a hard sell to charge for services that the clinic down the road is providing for "free", even if the total cost of ownership is the same.