Please watch this video:

If you want to skip just go to around 1:30 or so

https://www.youtube.com/watch?v=7wDmoUm5VCI

6.0's are one of the most unreliable engines i know of. I have an 04 f-250 with the 6.0 and my god do i hate it, it brakes down practically every week and its always a new  problem. Now if the engine has been bullet proofed then i would say get it because once bullet proofed they are not only very reliable but also very powerful. So in short ask if it has been bullet proofed and search as hard as you can for complications that the engine has and if it is bullet proofed and runs well then id say get it otherwise avoid it.

Such a shame that someone would get an 03 F-250 without the 7/3!!! (03 was the last year of the 7.3L Powerstroke, best engine in history) I believe the 6/0's have a history of problems, but they aren't terrible... I'd have to see it to appraise it but I wouldn't necessarily recommend it. Look for one with the 7.3.