Buying 2005 2500 6.6L Crew Duramax??

I was thinking about buying a truck as was looking for advice on what to check for when testing it out? I was planning on using it for towing a trailer and general day to day stuff. Short trips mostly unless towing the trailer.

I haven't seen the truck yet, but guy said it has 168,000km, tow package, power everything, box liner, needs brake job, just had rear axle seals changed
$23,000 CAD or roughly $18,000 US. I wasn't sure if there were any particular common issues with these trucks and was hoping someone could shed some light on it for me. I am coming from a 02 F150 5.4L Crew with lots of serious engine problems, so I am a bit gunshy now. Any info would be appreciated...