Transfer case, Thermostat, Water pump, Serp belts, fan clutch, air bags on the air ride suspension, sway bar links, electrical, wheel bearings, the list goes on and on....a lot of the issues are common and sometimes frequent. But remember...it's a vehicle and like any vehicle in the world ANYTHING can break or be a reoccurring issue. Check for the wear and tear, how many owners it has had, where it came from(wet or cold climate) as in those areas rust can be a big problem. I'm not sure of the resources in the Netherlands, but we get a carfax of any reported history on owners, maintenance and issues it has had fixed. Check to see if it has decent tread on the tires...I have found here in the States(Iowa) that dealerships will put on new or lightly used tires which can mask any uneven tire wear...which could be caused by alignment issues or much bigger problems over-all.
Take your time test driving it all all speeds, dont let the radio run or the ac/heat to run while your test driving as they can tend to hide any slight engine noises, check for a ticking sound under the hood. After driving take your time to fully look the truck over, make a list of EVERYTHING you find wrong with the truck and either negotiate them to be fixed or lower the asking price. If you can get an extended warranty...do so. In most cases the extended warranties on vehicles are a waste of money, but a lot of TB owners and Envoy owners have had these extended warranties pay for themselves in the end.
Have a set price in mind, KNOW what you want to pay going in, KNOW exactly what you want from the color of the truck to what the carpet in the interior looks like. Check to make sure anything that is power operated works and works well enough to your liking. And as always be prepared to WALK AWAY if you do not get what you want. If they want to sell it bad enough, they will either chase you as you walk out the door or call you and tell you a deal can be worked out. And don't be scared to be firm, you don't have to be an a-hole but being firm in everything that involves buying a vehicle will help you not get screwed so easily(If your at a dealership) IF trading in another vehicle, GET YOUR KEYS back as soon as they are done test driving it...they can "Lose" your keys as a way to keep you in the dealership and keep you from walking out.
I hope this helps, like I said it's probably different in the Netherlands buying a vehicle than it is here in the U.S.
If you fall absolutely head over heels for a truck(like I did) decide what issues you can and cannot deal with. And get ready to learn how to DIY with maintenance on these vehicles, because I can almost be certain your going to need it lol I bought my 03 Envoy 2 1/2 months ago, and we have already fixed several issues with it and put some big $$ into fixing a lot of those problems ourselves, but again doing it ourselves with the wonderful help of this forum, we have saved a butt load of money not needing to take it to a dealership to fix it.
Oh and one more thing, if you have several TB's you can test drive do it...I test drove my first Envoy which was in a horrid accident, and then test drove a dozen more that wasn't destroyed at some point, and the difference was HUGE!! The first truck I drove was nice, but not what I was looking for over-all but it also taught me what it was like to drive a truck with major frame issues, as the frame was bent. Even if it doesn't have what you want, drive it...as you can learn a lot from each vehicle you drive. I love my truck more than I have loved any vehicle in my life...and even though it's a pain in the rear most of the time, I couldn't imagine owning anything else. My husband and I are looking at adding 2 more to our family a TBSS and a TB LTZ, one for him and one as an emergency back up vehicle in case our daily drivers are out of commission for an extended period of time.