I bought my Costco membership so I could buy a hearing aid, so call the cost of the hearing aid $855 if you must. That's still more than $2000 in savings. The free hearing test was performed before paying for the membership.

Sure, salary is an incomplete proxy. Each also requires a bit of real estate, support staff, and equipment. Both my optometrist and the Costco vision center have a larger space than the Costco hearing center. The Costco hearing aid area typically has one assistant (not an audiologist) working. The optometrist also has at least one assistant (optician).

I chose eye exams and glasses because it is probably an experience that more people can relate to. Proctologists are MDs ($389,700/yr), have more complex facilities and equipment, need more support staff (reception, nurses, aenesthesiologist), have more complex sanitary needs (proctologists perform surgery), and tend not to send patients home with custom-fit devices.

As for inventory - it very well could be that an optometrist does not pay for it up front.

> CostCo has a proud reputation for using their annual membership fees to provide door-buster prices.

No, they limit margins and costs (e.g., by limiting SKUs) to keep prices down; paid memberships build psychological attachment, but the $55/yr membership isn't paying for much in terms of lower prices.

Those membership fees provide the majority of Costco's profit, though.

Correct. They do indeed work hard to minimize markup margins. They also sell some items at a definitive loss.

And they attribute their revenue to the membership fees.

> And they attribute their revenue to the membership fees.

No, their profit is largely attributes to membership fees; their revenue is almost entirely sales (for the 53-week “year” in their most recent 10-K, $126+ billion in net sales, less than $3 billion in membership fees.)

Basically, Costco uses a giant near-zero-profit sales operation as a the key benefit to sell memberships, which are its profit-making business.