Step1
As far as the determination of value, the lowest estimate will probably be from the dealer from whom you plan to buy a car (especially if you have secured a good price on the new car). In the majority of dealerships nationwide, the average gross profit on a used car is higher than that on a new car, even though the selling price is less. Why? Because dealerships make it a point to get trade-ins at the lowest possible price to ensure a higher gross profit when sold. DO NOT trade your current vehicle until you have made a concerted effort to establish its value...doing so could cost you hundreds of dollars.
Step2
Get a "buy number": Another potential source of information on the value of your car is from local dealerships that sell that make. Crazy as it seems, a lot of dealers will pay more money for cars bought from private individuals than they will for trade-ins. If you have a Chevy Suburban to trade, for example, take it to a Chevrolet dealer and ask for their buy price. Tell them you aren't buying anything, but want to know what they would pay for your vehicle as an outright purchase. You really aren't going to sell it to them (unless, of course, they make an exceptional offer), but if you decide that you want to trade the vehicle, you will have additional input as to its value. In fact, if the dealer where you try to trade the car offers you less, refer them to (in this example) the Chevrolet dealer that gave you the "buy number."
Step3
Should you trade or sell? To some degree, that has a lot to do with the type of vehicle that you have and the level of your patience. Obviously, you will almost always get more money for your car if you sell it yourself (as you should--you sold it and deserve the commission!) The age and type of car has a lot to do with how easy it will be to sell. A 10 year old pickup truck will be extremely easy to sell, while a year old luxury car will be a lot more difficult to sell on your own. Why? For starters, most buyers for your 10 year old truck will be paying cash. No bank will be involved, no credit applications will need to be taken and the deal can be consummated on the spot. For your late model luxury car, most buyers will be financing, which can delay the sale at best (while the buyer applies for the loan) and can, in the worst case scenario, kill the sale (if the bank turns down the loan or tells your buyer that they are paying too much for your car). In addition, most buyers will feel comfortable buying the older pickup truck from you. A $25,000 car bought from a private owner, however, will make some buyers nervous. Time wise, you will likely be able to sell an older vehicle in a quarter of the time it will take to sell a newer, more expensive vehicle, since the size of the buyer pool goes up as the price goes down.
Step4
For many vehicles, you should definately sell them yourself. If you have an older vehicle, definitely try to sell it on your own. Make it as presentable as possible. Remember, reconditioning is another reason that the dealer will pay less for your car than you can get for it yourself. Recondition it on your own and put the money in your pocket. Minor nicks and scratches can be covered by an inexpensive tube of touch-up paint. Clean the entire car, paying particular attention to the interior--vacuum, shampoo the carpet and upholstery and use a vinyl cleaner and dressing on the dashboard. Wash and wax the exterior thoroughly. Total investment in dollars: maybe $25. Total investment in time: a few hours. Possible benefit: Several hundred dollars. NO ONE wants to buy a dirty car unless they can "steal" it. Besides, a clean car indicates a well maintained car, and well maintained cars sell for more money.
Step5
As mentioned above, newer vehicles are a little different story, but don't think you can't sell yours on your own. It most likely will take longer, but of course the potential gain is even more on a later model vehicle. Prepare it as above (make it shine!) and take out an ad in the local paper (small community newspapers are often very effective). Make a professional flyer for the car and park it where it will get the most exposure.
Step6
If you are forced to trade the car, be realistic but be firm. If you have a desirable car in good condition the dealer will pay more for it--if you push them. Clean, well maintained cars are often in short supply, so the dealer should pay top dollar for it. (They pay top dollar at auto auctions all the time!) Save them the trouble of traveling to the auction by selling them your well maintained vehicle while squeezing every possible dollar out of it as a trade in.
Step7
Get a Good Price on Your Trade-In Car here http://tradeincar.890m.com/
Novice 
