Knewnewsit is equally annoying to have someone at the shop question you when you know what you want. i have found with mounting you need to mark it with tape and clear instructions or some employee might decide you need the factory suggested mount rather then what you really want/need.
thankfully im too poor to actually buy something currently new or from a shop so i only deal with mounting once in awhile.
you would think people in the retail side would make a info print out with ski basics to help explain what realistic, rather then being tongue in cheek about being a douche to do your job. it's like when they are trying to sell you some parabolic skis lol like yea man i know that means sidecut and it's been around a long time. all smoke and mirrors, if you helped educate your customers you wouldn't have as many ignorant requests but the flip side is you also wouldn't be able to prey on that same ignorance to up sell a bunch of worthless crap.
I like this discussion so bare in mind im just starting a conversation and not attacking.
All of your points come down to the shops youve dealt with. Any of the shops i walked into in whistler did not prey on me and were more than happy to help. They asked enough pointed questions to know what type of buyer i am. At that point they decided where to take it. That is a good sales person. When you have a busy shop and a customer comes in and interrupts to ask a question that could have been answered by just looking at the store and where they put stuff it can cause frustration in the employee. You'd be surprised how many people ski 5 times a year on that once a year ski trip and do not have a clue about ski technology. Instead of thinking they are being a douche talking about sidecut you could let them know (nicely) that youve been skiing for a while and have seen skiing evolve over time. dont just say "i know what sidecut is, its been around a long time". More than likely that salesperson will just stop helping you since you apparently know it all. Go with the conversation and lead it to what you are looking for instead.
When it comes to spelling out where to mount your skis etc... i find it best to always ask where they would want it. if their response is "what do you recommend" i would give them my opinion only AFTER asking where they ski, what trails do they ski, how they ski. For the east coast, someone who skis Stratton (big wide open not very challenging terrain) may opt for a more center mounted ski) while someone who skis Jay, tighter woods, steeper, challenging may opt for setting the binding back a bit to provide more float and quicker edge to edge with less tail drag. Knowing the local mountains is huge. You can rattle off trail names or start a conversation about the terrain and pick up quickly how they ski.
Preying on customers does not build trust with a customer and that customer will not be a loyal repeat customer. Let them know you know what you are talking about by the questions you ask, knowing the mountains in your area and recommending the correct equipment for their needs. If they are adamant about a specific ski I will most definitely cave and let them buy it. Everyone has to learn lessons sometimes and it has happened a few times that a customer will come back in and say "you know i should have listened to you about the length" or type of ski.