^ + 1

Right before signing the paperwork, inspect the car. Doing it after signing is pointless because you've already bought the car. Doing the inspection post signing doesn't give the dealership impetus to correct any issues.

Make sure you do the inspection in the daytime. It's hard to spot imperfections when the sun starts to set. Bring along a pair of polarized sunglasses, preferably ones made for fishing with 1.0mm polarization on the lenses. You can pick a pair up at Wal-Mart for $10. If the dealership tried to hide any scratches by waxing over them, you'll see them.

Thoroughly go over the car from tip to tail. Look at the rims through to the calipers. Look into the wheel wells. Get down and look under the car. Open all the doors and inspect the door jams and weather seals. Start the car and let it warm up. Test all the switchgear. Test the audio system. Open the hood and look for any signs of leaking. Double check the condition and level of the fluids. Check the production dates on the tires. Go over every inch of the interior.

Hand write a rider to the sales contract that enumerates the defects you have found and that they are to be corrected. It keeps the dealership from dragging their ass fixing the issues. It also gives you the opportunity to reject the vehicle presented to you for another one.

If you want any small extras thrown into the deal for free, now's the time to ask for them. If the ignition key & key fob are super expensive and you want a 3rd set, get them to throw it in for free. Do you think you can get any other small factory oem accessory for free?

Make sure they give you all the manuals that are supposed to come with the vehicle. Make sure they hand you the wheel lock. Make sure one of the sets of keys they give you has the engraved key number plate.

I did all this when I bought my new car last week. I found some very minor imperfections and made sure the dealership addressed the issues. It also allowed me to haggle/barter a little more before the paperwork was finalized.