Research is everything
When it comes to purchasing a used car information is everything. Before I ever buy a car I do my research and make sure the car is going to meet my needs. For example I would pick a model that I would like to have and check with my insurance what its going to cost to insure it. Insurance on sport compact cars and compact cars is actually some of the highest insured cars to own where as full size trucks can be one of the lowest. If the insurance is in the budget I would move on to finding the cars value, to accomplish this I check all platforms to see what they are currently being listed and sold for. Some of these sites would be Cars.com or CarFax.com for dealership used cars or Facebook Marketplace, Offerup, Craigslist for private party used cars. I always sort by the least expensive option to know what the low end of the cars value is going to be so I know what a good buy is going to look like. Then I would also find the value of a particular car by using a website such as Kelly Blue Book, make sure to print your results for KBB, more on this later. Lastly I would use a VIN (Vehicle Identification Number) Checker such as Car Fax to obtain the history of the car I am looking to buy. This will let you know if the car has been in a accident that hasn't been listed or a recall issue that hasn't been resolved or title problems and odometer rollbacks. These items could be deal breakers or massive ways to negotiate.
Know what your buying and who your buying from
Hit them with an extreme anchor
When its time to talk numbers I bring up all the issues the car has (and they all have some) that weren't listed in the ad to remind them that their asking price was for a car not including these issues. Then I hit them with what's called an extreme anchor and offer them half of there listed sales price (this is for private party negotiations). What this does is automatically brings the seller to his lowest price he planned on getting for the car prior to the meeting. They will typically look let down or slightly insulted but they will reply with something such as $XXXX was the lowest I was looking to go. If you know what the cars value and issues are you can now determine if that is a good price or not. If the price is still to high I would show them the Kelly Blue Book value chart that you printed to point out that their expectations for the vehicle value are unrealistic (this can happen quite often). When you show them that they have a car with issues and its more than others in your area they tend to be more flexible on the price. Now that you have the vehicle at the lowest price I have one last tool that can help finish the deal.
Squeeze the last bit of juice
I have noticed that no one walks away from a vehicle negotiation over $200 as they do not really want to go through this sales process with another individual. They will most likely be close minded at this point but I would remind them that I am right in front of them with cash in hand willing to take their problem (vehicle) away and they wont have to deal with it anymore. Then they typically agree and you shake their hand and sign the paperwork. As a side note I know I may come across as insensitive or heartless but let me point some things out. If a car is listed at a low price (good deal) and the car is exactly as described with no hidden issues I happily pay their asking amount and both parties win however this is rarely the case. Most people sell cars because they are tired of the problems and are ready to move on. Unfortunately I find that most people will not list all the issues their vehicle has in attempt to gain more positive responses when selling or to obtain top dollar for their car. My logic is if the seller isn't forthcoming with the problems the vehicle has why should I be worried about hurting their feelings with a lower price offer than they were looking for, they always have the option to not sell you the car. Good Luck