There isn't enough mark up in audio equipment and lighting for these dealers to really offer more than 20% off...Especially if free shipping is included.
The Map Prices on audio gear over the past 9 or 10 years or so have been kept fairly low in relation to dealer costs. I think MAP prices were a good bit higher for audio dealers back in the 80s and 90s, and there was more profit in each sale back then.
When I bought the Yamaha DBR10 for my sister to use, they gave it to me at COST to beat out a Internet price I found. Cost was $308, and MAP was $399. Only $91 potential profit assuming customers come in and pay MAP. ....I paid $326 with tax that day. Dealer Cost is generally about 69% to 79% of MAP price on Audio Gear. Then consider if they have to pay to ship the item from a internet sale...I would imagine profits are slim on most items they sell when they are offering 17% off.
These audio dealers make more profit margin on stuff like Cables/Accessories etc.