What discount you can expect
I've sold middle to high-end audio and video for the last 12 years and can tell you that the discount that you can expect isn't wholly tied to the mark-up. Another factor is how the salesperson or the store gets paid on the sale. For instance, at one of my jobs my income on the sale didn't get reduced in proportion to the discount. Rather, after a certain percentage below list price, my income was almost halved.
For instance, more than a 5% discount on components and I'd get 1/2 of what I would have gotten had I sold them at full price. With speakers there was more room--say, up to a 10% discount--before my compensation was halved. With video the profit margin was so low that discounting didn't hurt me because I was making so little money to begin with. (As a matter of fact, the shorthand for anything that was low margin was "video.") The video is where you might want to seek your discount. Oh, and furniture also has good mark-up--better than speakers. You should be able to get about 15% off here.
Of course, the more vital question is whether you are getting the best value for your dollar? What good is getting 20% off the wrong system (e.g. poor value, poor system synergy, inappropriate gear), and spending 18k, when you could spend the same 18k on a system that fits you to a "T."
Also, 9 times out of 10, if you're dealing with career salespeople, which you should, (i.e. no Best Buys or similar "big box" stores) you will get more consideration during and after the sale if you're not "nickel and diming." Right or wrong, that's just how salespeople, sales managers, and store owners react. It's not really a question of the money buying the service, it's a question of offending them by not recognizing that their expertise is worth paying list—or close to it. This is how a lot of salespeople will take it when you look for discounts. By all means, try to get a discount, but exercise tact and good people skills. You may or may not get the size discount you want, but you'll maintain the good relationship and get the proper system design and service that goes with it.
Of course, if you are an expert and you really do know how to assemble your own system, even the better boutique stores will be more aggressive on pricing if you just come out and say where you stand. That is, tell them you don't want to take up their time, you know what you want, and ask them if you just hand over the cash can you get 15% off. If you're not looking for their support then or later, you'll get the 15% off—or thereabouts. Bear in mind, however, that some brands demand that dealerships don’t discount at all or that they don’t discount more than 5%.
The above approach will not work if the dealer is installing the system for you. If, as an audio/video store, they're worth the clothes they're wearing, they are NOT going to take your system design at face value. They will either thoroughly review your design or come up with one of their own--the latter approach is actually faster. Good design takes time and their expertise and has its price.
I hope this helped!
