If you’re going to view a RIB, there are forum members who may be close (I note you’re in the Netherlands) who may view with you if you put a shout out and they’re local. Second pair of eyes and all that. It’s still your decision, but they won’t usually be swayed by shiny bits like a new buyer!
Genuine owners will tell you everything, with paperwork that puts an HMRC inspection to shame. Have a budget in mind. View sites such as Boats and Outboards, Apollo Duck, EBay, FAFB, local brokerage or marinas to build up an idea of what you actually want and prices, otherwise it’s a lamb to the slaughter and you could end up with something that needs work or isn’t practical.
What are others using? I’m assuming it’s the North Sea or inland waterways? Are there engine restrictions, 4-stroke for example?
Hull angle is important too. Some leisure ribs have shallow hull angles, so slap in F4 or short chop.
What are you towing with? Sub 5m, then will be on unbraked 750kg trailer. Over that you’re into braked trailer territory. As mentioned already, trailer condition speaks volumes - you don’t want a smoking bearing or binding brakes 5 minutes after purchasing, heading down the road.
Storage. If you have space at home or is it going on hard standing at Marina. If you have a garage, consider height with A frame.
Engines tend to stay with RIBs, so if it’s older RIB, then expect an older engine unless it’s been repowered. Nothing wrong with that if it’s been maintained. Servicing wise, every year or every other year for impellers and gear oil. Most genuine owners tinker, so everything from replacement fuel connectors to thermostat gaskets will or should have been replaced with a record of when. If you’re spanner handy, then this will be a labour of love. Useful to build up knowledge as you progress. If you’re not, then consider an auxilliary engine, as a lot will depend on your RIB’s intended use, where you boat, frequency of other boat traffic.
You need a licence for VHF radio use. Quick search shows there are a few options in Netherlands.
Remember and post a few pictures up once you buy. Everyone likes to see a new RIB!