We bought a 2014 this spring and our surveyor didn't find half of what we ended up fixing this year. Our surveyor was not a good one, as we have come to learn, and he missed a lot of things. We are still thrilled with it and the deal we got, but we were working on something almost every time we went out.
If you intend to trailer the boat, make sure a trailer is included in your discussions! A majority of the 29's we looked at did not have one included and buying one is shockingly expensive. If you are getting a trailer with the deal, insist on new tires all around. We didn't and ended up replacing them before the sun set the day we towed it home. That was a rough day.
As far as things to check: The most important one I have learned since becoming an owner would be to get the boat up to WOT during the sea trial and try to hold it there for 15+ minutes to make sure you have access to the entire rev range and it doesn't overheat in those conditions. Both issues are very solvable and not a huge red flag, but that should be the sellers problem, not yours. A lot of owners of these boats have run them at 1600-1800 RPM from the day they bought to the day they sold, which isn't particularly good for the engine. Volvo says to get the motor running close to WOT periodically to help burn out soot ect. When we first got ours we would get too hot at 3000 rpm, did a rydlyme treatment and habitually did hot runs to work the motor up. Now we never get hot but we only have access to 3300 rpm. It's been slowly improving as we use the boat more at speed, but we have a ways to go yet. Make sure the generator starts up easy and can hold a load for a while. The previous owners hardly ever ran it and it requires quite a bit of work (time, not money, luckily) to get going again. Outside of those 2 items, most components are pretty easy to work on or replace if you have an issue with them, so if the deal is good and you don't mind putting some work in you can do pretty well for yourself.
Good luck to you! It is a truly special boat and I hope you get to enjoy it as much as we have enjoyed ours.