I still say a majority of the decline can be attributed to generational proclivities. There's virtually little to no input from any of the thirty-somethings in this thread.
Blaming "tire kickers" (the first I've heard this term applied to audio shoppers was in reading this thread) wholeheartedly for this is unfair, just the same as blaming snobby salesmen.
I can see the issue from both perspectives but I have to offer an analogy of car shopping for further clarification:
The shopper knows full well what they can reasonably afford. Over 90% of the average demographic will purposely avoid entering a Bentley/Rolls Royce or Lamborghini dealership because there's nothing there affordable (this is the equivalent of visiting an audio shop you know has stratospheric systems in there that you know you cannot afford). You will, however, have persons that are either serious ("I want an S Class Mercedes S65 AMG Black Series with custom Designo leather interior, upgraded wheels and Burmester sound system") and those that are browsing (or "tire-kicking" as some pejoratively refer to them). The browsers, in my opinion, are comparison-shopping, as they have more than likely visited other dealerships and are looking for the best value for their money.
If you're wanting to purchase an upscale luxury vehicle, will you only visit the BMW dealer if you don't know precisely what you want? Wouldn't you read internet reviews, watch review videos of the interested vehicles? Wouldn't you also visit Mercedes, Lexus, Audi? Someone will get your sale. You may have really liked the features and performance of the Lexus but the salesperson treated you as a "waste of time" so you decided to buy the BMW instead because, not only was the vehicle comparable but the service was more accommodating. The salesperson realized the customer was making an important decision and spending a large amount of money and didn't want to make any mistakes. True, this does not bode well for commissioned sales staff, but it's the nature of the business. You never know if that person will actually return and purchase from you because of your patience. Not everyone is a walking sack of money (even if they're in a BMW or Lexus dealership). The internet direct-order equivalent for something like this would be Carvana or similar.
Apply this to high end audio and you'll get a clear picture. The disadvantage of high end audio is the lack of financing options industrywide. This one aspect alone would expand the customer base (especially for millennials already wrestling with student loan debt). Until then, every high end salesman is Captain Ahab.
In other words don't go looking at a Focal Grande Utopia/Naim system with Martin Logan/Benchmark money. As much as I would want to hear a pair of Focal Grande Utopias, I couldn't just go down there and expect them to turn them on for me (if I don't know the owner). For sellers, don't write off a customer as a waste of time because they're just listening to a system. They probably traveled from out of state to listen to it, and if it is not an "appointments only" type of establishment, it makes sense to accommodate this because this person may return after they've done their comparison-shopping. Service is expected to be paramount in brick-and-mortar establishments. Not every customer that walks through the door of an establishment will buy something. Maybe that's my millennial logic.