Welcome to the campfire.
Since you are asking what to look for I would highly recommend that on a used 2 owner unit that you seek the services of a qualified RV inspector to do a complete inspection top to bottom.
If you elect to ignore this recommendation and go on your own;
- Check to make sure all systems are functional and this will require de-winterizing the unit so all of the plumbing can be checked for leaks.
- Make sure the hot water heater works on electric and gas which means it will need to be checked one way, drained and the checked the other way.
- Verify the age of the tires. A 2014 unit will require new tires soon (based on ager) unless they have been replaced.
- Verify the age of the chassis and house batteries. Same thing applies with age.
- Take the unit for a good test drive that includes city and highway driving. Make sure you are comfortable with how it handles. Do this even if you elect to hire the RV Inspector.
Hope this helps and good luck.