That’s a problem not limited to purchasing hearing aids. I had a similar (but even trickier) issue with purchasing a Garmin GPS. I received a tracking number, and then a verification of delivery. However, the delivery notice stated that it was “signed at the front office”. The problem with that is that there is no front office, I don’t live in an apartment, and no one had been to my house (I was home at the time). I immediately filed a claim with eBay. They reimbursed me, and no problem there.
I did some research, and found this is how the scam works. Someone sets up a new account, advertises something at a good but not ridiculously low price, then ships a package that’s just an empty envelope (or junk in the envelope). They pick out a business in the same zip code, knowing it will be routinely signed for by someone in receiving or a front office (in my case, the envelope was delivered to a local retail store). They can then “prove” to eBay that the package was delivered, which delays the claim process long enough for them to close their account completely, and keep their ill gotten money.
HAs are no different than any other purchase on eBay - be careful, check out your seller, pay with a payment method that offers a recourse if you’re scammed.