The whole thing sucks. or blows. Or deflates quickly. I have bought inflatables new and used, and I would have said I have far better luck with used AIRES, but even they can have pinholes in the pvc, or repairs that do not hold up as well. I have a JPW culebra that is one of the first bought new 12-14 years ago) and I have blown out a foot cup and that is it. Used gear is tricky. If the price is too good, and the story does not match the reason it is being sold, or if the item is too old (very different per boat) run. It sounds like the seller knew a bit more than disclosing, but the buyer should have been suspect about the straps too, on the culebra the straps live under the boat, away from the sun, so there really ought to be a good explaination for it. If the tubes can be patched and salvaged the culebra is a dynamite boat. It surfs great, gets up to speed fast, and can be thrown around really quick. It has been all of my kids introduction to whitewater because of the ease of R-1.5 it( and you can even override someone throwing strokes. )
I think the big lessons are
1) Get the serial number in advance, have the seller send a high def picture of it. Call the manufacturer and get a manufacture date, also sometimes they will disclose if it is at the end of life too. They can also give you a bit of beta on the boat too. I managed to find a lynx 2 that spent some time in Japan. Crazy stuff...
2) Inflate to full PSI, get out a lawn chair and wait. If it is going to be a day boat, 45 minutes will be telling, if it is multidays, you may want to bring a book and wait longer. Seeing how bad a leak is, and how hard it will be to top off on the water is important. We had a very old boat that we named bubbles for the huge number of leaks. Topping it off every 40 minutes. We got it used, with a frame, oars and other stuff, and sold that stuff to cover the cost of the boat. When we got rid of it we fully disclosed the issues, and someone wanted to try to repair it, I think we may have even given it away.
3) If the accessories are not in the same shape as the boat or claims about the boat, be dubious.
4) You need to have a clear story about the boat, why it was being sold and to trace its history to the best of your knowledge.
5) never pay ask for any small engine purchase that is warm when you show up. You always want to start with it cold.
6) you can re-coat pvc, but it is a miserable experience, you need a full respirator, and clean shaven face for a good seal, and get to use fun stuff like xylene and tolulene. I personally will not ever do that again.
Good luck with the boat, sorry for the rough purchase experience. Not all used boat gear sellers are problematic.