Buying a used big rig is a gamble. But, it is possible to get a good deal on a decent used truck if you do your research. I’ve only bought used trucks a few times.
Make sure that it has been well-maintained and has the engine and driveline specs suitable for your needs.
– Copies of the maintenance records – How often was the oil changed? – Who maintained the vehicle mechanically?
Personally, I would prefer dealing with factory dealers, rather than large volume used heavy equipment companies.
Extra warranty through a dealership is often an option and certainly worth researching. Sometimes that can save a lot of grief.
Learn to recognize the earmarks and manufacturers of these kind of trucks. Look at the quality or lack thereof the initial build.