What is the average dealer mark up?

@dill:  I typically do buy on-line and am not taking up salespersons' time needlessly.  I know that in my locale the available audio stores will not carry what I want.  I bought used Parasound amp and drove to the next state to pick it up. I bought a used Parasound pre-amp online and had it delivered.  Now, I spent a bit over $2,000 for the pair. Could I get those items in local stores? I don't think so.  They would be selling new equipment for thousands more, or selling new equipment with less quality, or I could take my chances finding what I want at a pawn shop.  I don't see local purchase options that come close to what I find on-line.  Maybe in a major city the options would be greater and I would shop B&M.

For the 10 years I worked part-time in the business, mid-fi and high end, it was 40% for speakers and 25% for electronics.  Accessories and cables higher.

I just talked to my local dealer a couple of days ago.  He said they are doing fine.  They are appointment only right now.  I live in a small city and there are only 2 dealers in town.  I believe that he is still paying his employees as well, at least he was when this started.

I am a bargain hunter but I also appreciate B&M and am willing to pay more(to an extent) to support them.  My dealer does things right.  He will let you take something home for a week and try it in your system or bring something in and listen side by side.  I recently bought a nice integrated and I went with his recommendation(which wasn't even on my list initially) because I got to try it out with my own equipment.  I won't buy everything there because I like a good deal too much, but I will ask his opinion and give him the opportunity to get my business first(which he appreciates.)

It all depends on the overhead of the business. If your fixed overhead is 20,000 a month less payroll, that is factored into the price of each unit sold. If that causes the price to be too high then the business will close.
This is why there are so few left. Our Audio business is in its 80th year. I hope this helps. 

Do not confuse mark up with profit!  From that mark up all overhead has to be paid BEFORE a profit can be realized.  Even if the retailer is strictly online, there are significant expenses that have to be paid first before the profit kicks in.   And once there is a profit, then taxes have to be paid on that.