When I went to pick up my CPAP machine, we went through the standard 1+ hour spiel in 10-15 minutes as I could tell him what he was going to say next.

My wife has had a CPAP for 9 months, so I was pretty aware of all the details.
When it came to clinical menu items, he said he "wasn't allowed" to tell me how to do that and would cover his eyes while I did it. All in a very friendly, supportive way.
Later, when we went back to the same DME to swap my wife's CPAP brick for an APAP, he wasn't there and we had to deal with a sales manager from the main office. Who proceeded to lie to us about the difference between different AUTOSET models.
It depends a lot on the individual RT!