Good thread - I'll try to contribute where I can.  I've worked in the car business for 10+ years first on the dealer side and then for Ford.  I've touched every aspect of the business.  Couple comments based on the previous questions in the thread.- New Cars - Margin is probably 6-12% between sticker and invoice, based on price.  I've seen 14K base B-cars with a difference of less than $300 to $50K vehicles with a markup of around $6K.  Under the line money includes holdback (traditionally around 3% of invoice).  This is money given back to the dealer to offset interest charges.  Most dealers will use a line of credit (floorplan) on their new vehicle inventory.  The holdback should cover 3-4 months of interest payments.  Luxury manufacturers are moving away from holdback over the past couple of years, and are moving to other forms of dealerhsip compensation.  Other charges included in the MSRP are destination charges (shown) and advertising fees (not shown).  Both are real charges to the dealership.  The ad fees pay for Tier 2 advertising (Tier 1 National, Tier 2 Reional, Tier 3 Dealer).  When you see the ad that was brought ot you by  "Your Valley Toyota Dealers" - this is an example of Tier 2 ads. They tend to focus on offers vs branding at the National level.Best time to buy a car is at the end of the month, best week is between Christmas and New Year's.  Extra money will be dedicated to Memorial Day, Labor Day, and End of Year for rebates.  "Truck Months", 4th of July, and Presidents Day are also times to bump rebates.Model years are becoming more convuluted.  New models will hit between January and November, there is no longer a clear cut line.  With many plants and product cycles, the timing is spaced out based on capacity, parts constraint, and marketing budgets.Doc fees vary by dealer and region and are justified by claiming they pay for title work and other back office operations.  They are a common practice but I've seen fees range from $80-$800.Used Cars - You will get more money by selling it on your own, but it may not be worth the hassle.  Dealerships are set up with a much larger selection, financing options, service contracts, inspections, and a physical location.  Selling your car yourself means you need to market the car, sell it "as-is", go to the bank with the purchaser, and hope the guy doesn't come back to your house if something breaks on the vehicle.Older or high mileage trades - most good new car franchised dealers are not interested in vehicles over 80-120K miles or over 7-8 years old.  They are harder to finance, warranty, and sell extended service contracts on.  Why risk your reputation selling a 10 year old car with 150K miles?  These vehicles will be wholesaled or taken to auction and land at a used car lot or "buy here, pay here" type facility.  Other examples are trading in a Porsche at a Dodge store - they don't have the market for a Porsche and will call a high line store to get a "buy bid".  Reconditioning - The average 50K mile car needs 4 new tires, new filters (oil, air, fuel), front brakes, a thorough detail, and possibly more.  An $8500 trade will get $1100-$1700 worth of work, and then be marked up around $3000.  The markup covers the people, building, marketing, and warranty on the vehicle.Trade Expectations -  Go look at KBB, look at rough trade.  This is a starting point.  If it is a hot car, you may get more.  If gas prices are spiking and you are in a Tahoe, expect less.  By nature, these sites are trailing indicators.  The dealer is at auction at least 1x/week. They do have a better idea of market value.Negotiations - If trading, always work a difference figure.  I don't care what the pricing is on either car, I just want to what the difference between the 2 is.  20 for yours, 12 for mine is the same as 16 for yours, 8 for mine.  Your payoff on your car has no bearing on what your car is worth.  If you owe 15K, it doesn't mean your car is worth $15K.  If you had paid cash, would your car be worth zero?  Dealers will ask about the financing of your car to find out how to structure the deal.  If you financed for 60 months last time, bought a warranty, had a $450 payment, you'll probably be OK with that again.  And you would likely pay $30-50 more to go from a 4 year old car with 60K to a new car with no miles.More later.