Suzumar are really good boats, and at 3.2m its a great size for a sib. Boat is not quite as good quality as the Zodiac but streets ahead of all the others you have mentioned.
These boats have welded seams so should hold air for years, however the rest of the boat is held together with standard PVC glue. Glue on all makes of PVC boats has a life span of about 10 years (this is not an exact figure, but a good approximation), at this point the glue degrades so much it starts to fail. Things start to come loose and eventually the floor drops out or the transom falls off. All of these things can be repaired pretty easily using 2 part glue, but it takes time and patience.
The other enemy of inflatables is sun (not a big problem here in the UK
), if left in direct sunlight for extended periods the material goes brown and starts to degrade and even delaminate. It also seems to speed up the glue failing.
Check out the boat carefully, look for signs the glue is failing on the fittings (D rings, safety line, oar locks etc), check for signs of sun damage and then negoitiate accordingly. Only buy and older boat like this if you are quite handy with repairs, or can pay someone else to do it.