I think you need to add another category to the options. I guess it would be mail order (but not ID)...to include Accessories4Less, Crutchfield, AudioAdvisor, Amazon, Parts Express, Audioholics Store
, etc.
And, I have spent a few dollars with Pro-Audio companies like Sweetwater and Musician's Friend (which I guess could be grouped with mail order).
Everything included, I have bought much more gear through non-ID mail-order than any other single category of seller/reseller.
Then there is the used market through Audiogon, Craigs List, eBay, etc. Which is the best option for those with the experience, knowledge, and time to find and know the deals when they present themselves.