I was in the auto business on the corp level heavily involved with dealers. Invoice does not mean nothing. I know all about incentives both public and private. It is more complex than you will ever know unless you are immersed in it.

Invoice is a way to compare the deal from dealer to dealer. When you talk OTD to a dealer they see you as a sucker. Not to say that you can't get a good deal by negotiating OTD but you are firing in the dark. When you go in with a deal relative to invoice then you have a better barometer of the deal.

Best strategy is to contact the dealers in your area and give them an "X below invoice plus incentives" number and see what comes back. Be liberal with the X number, try $2000 to start. I do something a bit more sophisticated but you should almost always out deal and OTD strategy this way. Then negotiate trade-in, then fees (when appropriate) and then financing.

Take it or leave it advice from someone who has seen behind the curtain. Good luck.