Good points, but it's not just about cost. With my real world case of the 140 pound sub just packing it up and getting it to a point it can be picked up by a shipper (like the garage) is most of the PITA. It would take another strong person to do it, and a well-muscled young man is never around when you need one. (He lives in another city.)
I could have saved $400 on the DD18+ by ordering over the internet, albeit from a non-authorized dealer, but $400 out of $4200 just wasn't enough. Anyway, the contender at the time was the Funk Audio 18.0 or 18.3, and FA doesn't offer a money-back guarantee.
I agree audio shows can be a resource, but I've never been able to make a speaker buying decision by what I heard at a show.
For electronics ID can be the way to go, but even there I'm cautious. For example, let's take the case of my Emotiva ERC-2 CD player, which I'm just using as a CD drive. I paid $369 for it, thinking, how could I go wrong for that price? So I bought it unseen. That turned out to be a mistake. While the ERC-2 is indeed a remarkable value in sound quality, even at its current $499 asking price, it is not ergonomically acceptable to me. The Toshiba CD drive is slow, noisy, and clunky. The button controls are cheap to the point of unreliability, and you often have to press some of them twice. The remote control has sharp aluminum edges; be careful with it on fine wood furniture. Truth be known, if I had a chance to test it in person I would have never bought one. I've ordered an even cheaper Tascam CD200 to replace it, but I've seen a CD200 in person, and it is indeed ergonomically superior.