The only way you know what the margin is will be to leave your checkbook stick out of your pocket so the dealer knows you are serious and then make an offer. Refusal will be a hint that you are too low. Countering by a large margin tells the dealer he has you on the ropes so don't hesitate to walk away. Again, the visible check book may have him calling you back so you know you can't be too far off. Remember, this is all about the "Art of the Deal." You need to have done some research as to on-line and locale radio/tv ads for similar makes and models. Here is a technique I've seen work quite well. I once attended a boat show with a neighbor who was a heavy equipment purchaser for a municipality. He was well versed on the "low bid" process. He was looking for a 16 foot utility boat, 15 HP Johnson/Evinrude/Merc/Yamaha. He prepared a bid sheet with everything he wanted including a trailer, anchor, etc. We went to the boat show, and handed out the bid sheets that clearly stated he had the right to refuse any and all bids. Informing each recipient that he would be back in three hours to collect the bids. About 2/3 of the dealers were amazed when we showed up and admitted they didn't think he was serious. After a scolding, indicating he didn't spend the time preparing the bid sheets, pay to attend the show, and distribute the sheets just because he had nothing else to do. Having researched the products he was most interested in it was relatively easy to determine what an acceptable deal was. Remember, you will never ever know exactly what the margin is with any one dealer because of the turnover at his dealership which tends to give high volume dealers a distinct advantage. Only you can determine what an acceptable price is and once you buy -- stop looking. Sooner or later you may stumble on a better deal. As a result of this exercise, a Lund dealer provided the information, an acceptable price and the deal was consumated then and there. This is only one technique but you cannot know what is even close to reasonable unless you do reasonable research. Visit dealers in the surrounding area and actually try to act serious. Nothing happens until you write the check so you are free to walk away anytime.