Average_joe does his own impressions but for 99.99999% of people, I would very strongly advise against DIY impressions, because it's extremely tricky to get the foam dam in one's ear canal to exactly the right position and (more importantly) it's almost impossible to know if the dam is successfully placed so as to prevent silicone from squeezing past it. There is a very good reason why a qualified audiologist will use an otoscope to check the positioning of the foam dam, prior to injecting the silicone. If silicone gets past the dam, then the dam is useless and you risk the silicone sticking to your eardrum and your eardrum consequently being ripped out of your ear canal when you withdraw the cured impression from your ear.
It doesn't stick, but yes harm can be done. A vacuum could form, and in theory damage could be done during removal. Worst cases I have been remotely involved in, the silicone passed over the dam, interred the middle cavity via a hole in the ear drum....
This happened in Thailand, so no lawyers were involved
And no it wasn't me, I just got a phone call from a person in a panic asking what to do about this situation
One word response... Hospital