The only dickering on prices I know of that I can do are on a new car purchase. The last time I bought one, I did all my research on the model I wanted and my trade in and arrived at the difference I was willing to pay the dealer in cash. As always, the salesman kept makng trips back and forth to his manager, but finally we arrived on an agreement that was $400 off from what I'd hoped for. That was close enough, so I took it.
Negotiating gets more complicated when financing is involved, or the model I want has different options from the one offered. When that has happened in the past, I get all the information and tell them I have to think it over and return later. Then they try to make it seem it's a "now or never" deal. In that case, for me it's never, and I go elsewhere.