My experience is that stores will sometimes refuse to lower the listed price -- but they will (if asked!) be willing to include 'freebies' related to the purchase:
. . . a stand;
. . . a gig bag;
. . . sheet music;
. . . a pedal (to replace the "stock" Casio PX-150 pedal).
Also, I suspect that a $5,000 price is more "negotiable" than a $500 price. The higher-priced item is harder to sell, and carries (probably) a higher profit margin for the store. So there's more "wiggle room" for the salesman.
If you don't ask, you don't get.
When I bought my DP, I first of all made sure that it really was what I wanted, then asked the dealer what he could offer if I bought it there and then. Once he realized that I meant business, he was only too keen to make me an offer I couldn't refuse
. Without my prompting, he also threw in an excellent pair of headphones (though he'd already seen me using my own Bose ones, which he felt was more suited for travel listening than DP playing). Then I asked him how I was going to play from the music.....and he threw in a music stand too.
I couldn't think of anything else I could push him for, despite racking my brains