To use the example of the OP (“mid level audio equipment”)
most/many electronics lines will have a 40% margin to the dealer. A well
run/efficient dealer will probably have a COB (cost of doing business) of at
least 25%. So, when you walk in and ask for a 10% off the dealer is left with
+/-5% profit…
As pointed out prior, a relationship with the dealer is important. If you walk in and state that you know exactly what you want and the dealer/salesperson doesn’t have to burn any time with you then 10% might be realistic. A turntable/cartridge properly set up by the dealer probably would not qualify. If you require a protracted demo(s), hand holding, couch time (analysis), then maybe asking for 10% is too much…