I've always wondered about this myself. When I was selling audio gear a long time ago, I was paying roughly 45-55% of the nonsensical "list price" on most receivers at the high end, when a model was introduced, and sometimes as low as about 20-25% when they were having their "These have to go!" closeouts.
One of my really popular models went for $599 normally at the local dealer, and was on sale for $499. I bought them for $212, and charged $400 and sold all 14 or whatever I bought in a few days once word got out. It was funny, but the brand I got the best deals on, Panasonic, were the most trouble free, by far, of all the brands I sold. HK was the worst with component (caps usually) failures, followed by Sansui with all kinds of truly bizarre issues with wiring and cold solder joints, and then Pioneer and Kenwood, with lots of bad soldering of the front panel pots. My Panasonic returns were almost nil, and when it happened, it was almost always a DOA, or it died in the first few minutes. The having to test most of the other stuff to avoid surprises got really old, and made my room almost unbearable due to all the heat coming off stuff just sitting there cooking away.
I would imagine the numbers haven't changed a whole lot since then, but the pricing is much more cutthroat these days.