I am a retired territory sales manager (not in audio) who saw, over the years, how some business persons "get it" and are successful no matter where they are, some are lucky enough to have a great location and are successful until they aren't and others never "get it."
Retail is a please the people business - if you're selling something they want or need at reasonable prices and don't treat your staff and customers like sh*t, odds are you will do well. But the potential market for any sales category decreases with higher prices as you have fewer potential customers, even with liberal credit policies. The Porsche dealer will rarely have more potential customers than the Chevy dealer. That said, if you sell enough Chevies, you can make more $$ than the Porsche dealer, you just have to have more transactions.
Repair work and installations are more profitable, in the long run, than straight up retail sales in most markets and that's why the OP and others are running into the gone on an installation signs. That's the reality of business these days as it's the only way for many dealers to add value and profits.