Can you trade in a vehicle if it has engine troubles and needs new tires?

First you go in and price out the new vehicle you want at several dealers using the "manufacturerer's invoice price" to start the price negotiation. Then you select the dealer that gives you the greatest discount below the "manufacturerer's invoice price". Typically you may negotiate $500 below invoice BEFORE you deduct any current manufacturer sales discounts being advertised. Once all that is complete (never having mentioned a "trade-in" if they asked you if you have one), THEN at that point you request a value to be deducted from your best deal above for your tradein. Guess what? They'll typically say "your vehicle has no value to us".