What is the average dealer mark up?

I rarely shop at retailers for the same reason I dread going to car dealerships — I feel like the salesperson and I are on opposing teams.  I want “best bang for the buck”, and I am not a lavish spender like someone who expects to pay $10,000 for a pair of loudspeakers or $125,000 on a Porsche.  If I go into a hifi store, I expect the staff to try their best to up-sell me on a more lavish system than what I want, and while I don’t mind looking, I know what I want to spend and that might not even be worth the salesperson’s time.  I want retailers to be able to stay in business, just in general, but I don’t want to consider what they need to pay rent or keep the lights on, or pay for staff, when all I want is a good deal.  There is a high-end audio retailer in my town, but I have never been there because I assume that I can get what I need, for less, and not have anyone try to talk me into a home theatre when all I want is stereo music.  I have been in stores in which the employees obviously see that I am not spending the kind of money they need to bring in, and I don’t like disappointing people.  

@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.