It is acceptable to watch and ask questions. You can learn a lot. In addition you should ask a few questions without being a pain
For example, " Have you surveyed many of these 248s? Are there specific things to look for?
If the surveyor mentions an issue, ask if it needs to be taken care of now or can wait and what do the surveyor think the repair will cost. For example, old hoses will need replacement eventually. Leaking hoses need repair now.
If you are experienced driving similar boats, you can ask the seller if you can test drive. If you are new to boating, maybe you shouldn't drie but if so do it in open deepish water areas.. The seller may also be on the boat during the sea trial. If so, I prefer to have the seller operate the boat until in open water. Then you can take over. Same for returning. The surveyor should also drive the vessel. The surveyor is looking for handling or operational issues, you are checking out the general look and feel. Maybe you can't see over the helm. Maybe the boat rolls more than you would like. Maybe is has a wet ride.
The absolute moisture readings are not as important as the relative readings on adjacent areas and the more the merrier Make sure the surveyor AND you note when the hull was last wet or if it was hauled very recently. Make a note in addition to the make and model of the surveyor's meter. If the surveyor detects excessive moisture, ask if he or she can take inside the hull measurements to confirm extent of moisture ( these readings can be tricky)
In addition to the hull and transom, the survey should generally test the deck, lockers lids, helm bulkhead maybe etc. If no readings are excessive, I would think his meter was broken
If it is raining, you can't do moisture tests.
Ask the seller if he or she normally uses the aux tank and replenishes its gas. If not, don't try to run on it.It may have gunk or bad gas. Ask the surveyor for his opinion.
Not also that surveyors often don't do motor surveys. If you want one, you probably will need to hire a mechanic to do it. That motor on the plus side is pretty reliable historically but is relatively old on the negative side. Get the surveyor's opinion on general performance. Before starting it, ask if it has been started that day before the survey ( or feel it for warmth). Pre warmed motors will often not show idling issues it has when cold started. SX motor often have rough idling issues when cold. During the sea trial, do at least a short run to WOT. Note the revs and speed ( using GPS, not the speedo).
Note the models of any navigation equipment and/or sonar.
Test every switch, light, horn, gauge. If there is a windlass, test that also.
My general guidelines for older boats is this;
If the boat is dirty, moldy and worn, there is a decent chance the owner neglected the motor and mechanicals also. On the other extreme, if the boats look too clean, new waxed, etc, it may have been detailed and that always raises an alarm for me.
Don't let you desire to have the boat blur your senses. Be thorough in your appraisal. Remember that little things like old cushions, old or missing canvas, hull damage etc. can cost a lot to repair. Take all that into consideration when deciding.
I probably forgot many things but for now I think you get the idea.
I hope it goes well, good luck.