“Any” can but many won’t. I have direct experience with three different audiologist who would not program or accept me as a client if I wanted them to work on used HAs that I bought off eBay, except the pair that I bought new from South Korea. They would work on them including sending them to Phonak (but no warranty).
Hint: when buying used HAs (from anywhere) obtain the serial numbers first and either plug those numbers into the Target software and check for warranty coverage, or call your friendly local audiologist and ask them to do it. If Target responds with “contact customer service” there is NO WARRANTY.
There are a pair of P90-R used HAs on eBay this moment that shows the serial numbers and current warranty period for another couple of years. These would likely be valid HAs (ie not recorded by Phonak as either lost, stolen or sold outside the USA).