IANAL, this is not legal advice.
An adjuster can be from your own company, independent or from the other party's company. In any of these cases, their job is to settle the claim for as little as they can, while still staying out of court. I suspect that is what the other poster meant by they aren't your friend.
An example from my situation. A woman pulled out in front of me resulting in an airbag deployment and my car was totaled because the right front wheel and axle shaft was shoved into the engine block on a 7 year old car.
Often times they exert "pressure" on the claimant in a number of ways. A low settlement offer very quickly with phrasing with push-back like "It may take quite a bit of time to go back and review your proposal" or similar. This works often because people are not buffered and need the money and they take it. Mustachians should be able to float the timeframe to not let this tactic work. They did this to me (my own carrier), I refused the first offer, it took an additional 2 months to review my proposed settlement.
Document values on your own and question how they came to their conclusions. If they total it and have an offer, ask them where you can find a comparable vehicle at that cost. Ask for a specific listing they are referencing. If they cannot find one, find an equivalent listing in your mind and ask for the higher amount. This is how I justified my higher amount. The value they gave me would only have purchased vehicles with many more miles than the one I had, and they couldn't find one with similar mileage in my area at a price lower than my proposal.
There were two offers of settlement in-between that I refused, each coming closer to my amount, talking about documented "sales." I said at each of these "Great, show me where I can buy a similar car and we are good to go." They couldn't either time. They also pulled the second pressure tactic on me: pulling the rental car. After the first offer they told me they were going to pull the rental, I said fine. Then they let me keep it. At the second offer they again said they were going to pull the rental, I said fine again, and they did pull it. I had another car so just let them. I was riding my bike to work, so my wife just kept using the other car. The rental was rarely used anyway. This really flummoxed the adjuster. He didn't comprehend how not having the second car wasn't going to be a huge inconvenience and tried multiple times to get me to take the offer instead of having to be so "inconvenienced" while he worked through my proposal. They finally came up to the the value I originally suggested and I accepted. I thought about asking for interest on the amount from the date of the crash, but opted not to push my luck. There were no medical injuries in my case.
If you have medical injuries, be VERY WARY of endorsing any checks. READ THE BACK CAREFULLY. Some carriers have an agreement on the back of the check that states that endorsement of the check constitutes agreement that the claim has been settled in full. For anything but totally minor injuries, I suggest you seek legal help to be sure you don't get worked over.
Good luck!