We all hate reading stories like this. Sorry for the troubles you're having with your new-to-you camper. I'm not a legal expert but I think your issue has little to do with the fifth wheel but everything to do with full disclosure laws in the state where you made the purchase. I would try and learn as much as possible about that, and then approach the RV dealership owner with the information that you found out from the previous owner as a place to start.
Others with more helpful information are sure to contribute.
2014 Micro Lite 19fd
2015 F-150 5.0L V8 XLT Crew Cab, 4x4, Tow Package, 36 gal tank, 3.55 locker, 1891 payload, Integrated Brake Controller, Roadmaster Active Suspension
Wooden Spoon Survivor