Looking at a used 2006 FX4 with 150,000 miles, auto. Any heads up what to look for? I have to travel 250 miles each way to have a look.

 

All your basic stuff.

Look for rust (under carriage as well as the body), listen for any strange noises during the test drive, make sure the steering is tight, drive it hard on the test drive (babying it isn't gonna show any issues), make sure the ball joint/tie rod end boots aren't torn, etc.

 

When you turn on the key make sure CEL(check engine light) comes on.

Test 4high and 4low

Look at clutch and brake pedals, see if they match the miles

Call Ford Dealer in closest town and ask how much for a Used Car inspection, usually $100-$150.
After the test drive if you are still interested, ask if he would mind if you paid to have Ford dealer inspect for $150, it's good if you know the price.
You don't need to do it, although it is worth while, you are mainly looking for his answer.

 

X2 on this.

Once bought a truck that had electrical tape over the check engine light. Was not a good experience.