chobit

I have done both private sale, and dealership trade.
First, reserach on market value for private sale on a car with the same condtion as yours.
Then, check with the dealership on trade-in value.
Don't forget to factor in the tax saving for your trade-in.
eg. if your car trade-in is $10,000, and you are buying a car for $25,000-  You pay your tax only base on the $25,000-$10,000 = $15,000 x tax rate.

So, if you sell private for $12,000 vs $10,000 trade-in, even with just 10% on tax, you are only making $1000 more by selling privately.

However, some cars are easier to sell than the other.  And some dealer do rip you off on trade-in.

Another thing is, learn to negociate your price on trade-in and the car you are buying serperately.  Some dealer may sell you the car less, but also take in your trade-in for less, so at the end of the day, your are not really saving on your new car purchase.

Personally, I would approcah the dealer for the price on the new car w/o talking about the actual trade in.  Once you get to the price you like, then talk about your trade, at this point you can decide rather you want to sell it privately or not.

chobit

My Miata has a trade in value of only $3500-, but I sold in privately for over $6000+ (don't remember exact amount)
My Subaru however, is not as easy to sell, and it takes  a long time to sell it for $31,000-$32,000-.  I remove my aftermarket stuffs and sell them for over $1K, then trade in for $29,000-  Tax saving at approx 10%, that's $2900+$29000+$1000 in value for my trade.

BTW, I currently live in Seattle, but used to live in Vancouver.