Investing time in potential customers must be considered a benefit, not a waste!
You just never know when the kid you talk to today may be the best customer in a few years with a large bank roll, and he certainly won't forget the time you gave him when he was a broke kid.
Furthermore, the people in these particular niche industries (audio, biking, etc) should be so passionate about their work that they actually like to discuss and educate, regardless of the $ at the end of the day.
I have personally been on the end of a salesman "profiling" me on more than 1 occasion, where he was clearly thinking to himself, "there is no way this chump can afford this stuff, he is wasting my time". Well, that a-hole lost a lot of $ and a lot of potential $ due to his preconceived world view.
I have also had the exact opposite experiences, and those are the ones that gain a customer for life, and possibly several thousand of my dollars.
One time I went into a bike shop, fairly early, just 1 other customer. I went in there to ask some questions and it was part of my info gathering looking for a new bike. The guy behind the counter was still drinking his morning coffee, and we had a long chat, he answered all my questions, and we started looking at some bikes and pricing at his dealer online connection (he did not have the style of bike in stock that I wanted). Other customers came and went, and the other shop guy handled that while we chatted.
Along the way of natural conversation, I discovered that this guy was actually the owner of the bike shop. At the end of about an hour of his time, I told him "get that bike on order, I like the vibe of this shop", furthermore, I ended up going for a step-up model.
So, I went in there just intending to talk, get some info, see what stock they had, and go about my day. I left with a deposit, a bike on the way, and an agreement to pay ~$1k for a new bike. Since then, I have paid that shop another ~$1k over the next few years.
That is a pretty dang good return on investment for an hour of chit chat.