Tires and batteries are no biggie. Yes, you need to have them, but every RV will need them at some point. Asking for a price break if they're due for replacement now is always good, but I wouldn't consider them a make or break deal.
Fridge - will it work on electrical? If so, then it could be something as simple as a new thermo-coupler (about $12 and easy to replace). If not, then that's a big expense most likely.*
Have it checked out for fuel leaks. Engine fuel (if a MH) and propane. These are usually easy fixes (replace hoses), but can be costly if the leak is in the tank or in the appliances. *A propane leak in the fridge could also be the issue there.
Check stove/oven, run both hot and cold water and check for leaking.
If MH, have engine, brakes, etc. all checked out. Even if told that the brakes were just replaced - get them checked (someone replaced the rear brakes in my clipper, but forgot to add brake fluid).
Be prepared to put additional money into it. Maintenance will be needed regardless of what you buy; repairs or replacements could be needed at any time as things age. Make sure your budget will allow for those costs as needed.
1975 American Clipper RV with Dodge 360 (photo in profile)
1998 American Clipper Fold n Roll Folding Trailer
Both born in Morgan Hill, CA to Irv Perch (Daddy of the Aristocrat trailers)