I agree with everyone else, negotiate on the OTD price only. In no particular order, my general rules are:
- Negotiate on final, OTD price only. As stated above, this brings all the BS charges to light right in the beginning instead of them slapping you with them at signing time
- In the early stages, negotiate on a POTENTIAL intent to trade-in your current vehicle (they will usually be more flexible on new car price if they plan on raping you for your old car)
- Always be more excited about the car's nearest competitor - you're there just looking at options... it's not your first or second choice vehicle. It's only the allure of a deal that's keeping you from walking into the other dealer and buying there
- Come armed with information like truecar.com info. Don't flaunt it, but be prepared to negotiate/argue intelligently.
- Bring a friend/family member to play good/bad cop with. One of you should be fairly unimpressed with the car. Think of buying a car like swimming with sharks and excitement is blood. The frenzy starts when there's blood in the water and it only gets worse with more blood. Would you rather deal with a mellow shark or a frenzied, hungry beast
- (Early stage) Be prepared to walk away if you're not getting the deal you want. Even if that deal is ridiculous, unless it's a rare, special edition, or dwindling stock of previous year models then you'll always be able to come back and buy it later or cheaper somewhere else. Waiting for the new car sucks... but not nearly as much as buyer's remorse
- (Late stage) Once your're set on a vehicle you want and you're in the last round(s) of haggling, ask for a simple, itemized list of the prices, fees, and charges... everything that will be a part of the OTD price. Ask questions. You can still walk away until you sign and there's a chance you can take these numbers to another deal and ask what their fees/charges are for each line item.
- Least important but potentially helpful - develop a rapport with your sales person and the finance manager. You never know when you might run into a fellow Lambda Lambda Lambda alumni or your sister's best friend's dad. It might buy you some points off the top or a bonus 'gift' in the deal just by building some shared camaraderie. BE CAREFUL with this one, it's a double edged sword and, at the end of the day, you might have dropped YOUR guard and now it's their turn to spin your mutual love of My Little Pony into My Fatty Commission
Also, to the point of dealer markup... this is one of the bigger reasons why the laws forbidding manufacturers from going consumer direct is BS. This is scalping, pure and simple. If the mfgr under prices the car, fine, let the savvy consumers buy them up and resell them. It's BS that dealers can mark up a product before its ever even touched the general market. It's very similar to insider trading, IMO.