Recently had to haggle with my insurance company about the value of my car after a tree decided to jump onto it and total it. I ended up getting what I wanted which was a few thousand more than they initially offered. You should first decide how much time/effort you want to put into arguing against their value. If you think its obscenely low, then I'd advise you to do the following
1. Start compiling lists and records of new parts, repairs, updates, etc. These will help to show that your particular vehicle was in better than average condition (if this assumption is in fact true).
2. Find listings and asking prices of other vehicles in and around your area that are for sale. You'll likely want to toss in a few of the ever-present excessively high priced vehicles. I did this as they noted a few of the lower end vehicles on their valuation which leads to my next point...
3. Before you formulate or tell them what you want value wise, ask for a valuation form from them. It should be detailed and usually from some 3rd party that they hire. It should include specifics including mechanical, exterior, interior, tires, add-ons etc. Typically they will include local listings in what they consider "similar condition" (which is why you need to do your own search to counter theirs).
4. Lastly and likely most importantly. Don't act like you are in a hurry and have to settle quickly unless you actually do. If they smell weakness, they'll sit on it and try to wait you out. I would get their valuation and then email your adjuster all of the above things including how you came about your valuation. Note that you believe yours to be fair and that you wish to come to an amount with which both parties can be happy. Don't get angry, just stand your ground. I went 4 months before I settled and on the day I eventually settled, I hadn't had any contact with the insurance company in over a month. Always be the last to respond so that they cannot say you ignored them and settle despite you. Just say something along the lines of, "I appreciate you offer but stand firm at my prior valuation which I believe to be fair." On the day I settled, the adjuster called saying that he was trying to get this claim closed. I explained that I felt the same way but that I was in no need to settle as I was already driving another vehicle which was paid for. He explained that he couldn't give me what I wanted and I told him I disagreed. 10 minutes after hanging up I got an email offering to settle for what I was asking for. Just know that they want to move the car and settle ASAP. Let them sweat it out.
