1967 Ford Mustang coupe on sale for $6000?
My first question as always is about rust. On a 67, check the floors under the carpet and under the car for rust. Also check under the carpet by the passengers feet, if it ever had a leaky heater core then some amount of rust will be there on the floor. Check out the trunk area (under the car and in the trunk) look at the METAL, if there is carpet in the trunk or a trunk mat, pull it up and look underneath. Check the frame rails for rust. Open both of the doors and look at the under side of the doors (where water would drain out) and see if there is any rust. The holes in the bottom of the doors often get clogged up with dirt/leaves, etc and do not allow the water to drain out causing the bottom of the doors to rust. The #1 area you want to check for rust is the cowl (the vented area between the windshield and the hood). Vintage mustangs were not properly protected in the cowl area. If the cowl is rusty it is a huge pain to replace the cowl. If you look at the car you can see all of the spot welds that would have to be drilled out to access the cowl, not fun. The easiest way to check if the cowl is leaky is to pour a cup of water into the cowl (between the windshield and the hood). Pour a cup on the drivers side of the cowl and see where it drains out. If the cowl is not rusted out then the water will drain out inside the fender and onto the ground. If the cowl is rusted the water will leak onto the interior floor boards (where your feet would sit if you were driving). Then pour a cup down the passenger side and check the same.
How is the paint? Be cautious if it is a "new" paint job. New paint jobs are often hiding a lot. Look closely all around the car for little bubbles in the paint (even if there is just one or two). Bubbles in the paint can mean that there is rust under that paint.
Pull the dipstick and see how the oil looks. Any seller with half a brain will have put fresh oil in it but check to make sure. Do the same with the tranny fluid. Tell the seller that you would like to take off a valve cover to see how it looks inside. Look to see if there is a lot of sludge built up on the rocker arms, push rods, and on the head itself. Take a peek at the coolant as well.
Does it have 4 wheel drum brakes? Drive at 40 or so and press the brakes like you are coming to a normal stop. While you are pressing the brakes, take your hands off the wheel. Keep your hands right next to the wheel but don't touch it while you are stopping. Does the car pull to one side while you are stopping?
If the car is a numbers matching (original engine, tranny, rear end) 67 coupe that runs good all around, has good interior, etc and all of the above things check out then I would personally pay maybe $5000 for it. If you know what you are shopping for, you can get a lot for $6000.