Read the fine print of the listing if you're looking online.  I bought a 3/4 ton pickup last month and had to negotiate just to pay the price that they had it listed for.  In the fine print they indicated the listed price was only good if you had a qualified trade-in AND were going to finance with them.  I was going to do neither of those so they wanted an extra $2,000.  I ended up getting them to sell it to me for the asking price and cut their documentation fee in half.  You have to make them think you are willing to walk away and not purchase it......which I was.

I've bought sprayers, drills, tractors, pickups, and cars off of website listings in the past 10 years.  I don't think I've had much success negotiating price but have used delivery as a negotiating tool.