I wouldn't buy from a rental place for the reasons mentioned above.
My Dad owns and RV repair business and you would not believe how bad people treat the RV's they own let alone people who rent them and have no idea how to use them.
Also, before you buy make sure you take it to a reputable place and have it checked out, there could be a lot of things wrong that you cant see just by looking at the RV. Such are dry rot. This sounds gross but act like you are flushing the toilet and take a good smell (you don't have to get real close) because if the black tank has not been taken care of properly it is very hard if not impossible to get rid of the smell that will come from it. Check the roof, people tend to let the roof go because they think it is good for 10 years. The 10 year warranty is only good if they owner takes proper care of the roof. Check the heater and refrigerator (no smell), hot water tank, converter, make sure no tanks leak, so they will need some liquid in them. Check to make sure the propane tanks have been updated with the new fittings or they tanks can't be filled. Check the walls and the floor around the walls for leaks, sometimes you can see the runs on the walls around the windows. If the floor feels spongy there is/was a leak. Around the toilet for leaks. Geez, I could go on and on...
Then you have the whole chassis to check also. Since I am sure you get the idea I will let it go...
Here is a tip for keeping a clean and smell free gray and black tank.....After you clean out the tank, put a small amount of water in the tank add chemical and a small amount of dish soap before you leave to go home. As you drive down the road the bouncing and swishing from the motion make the soap wash the inside of your tank and it wont hurt the tank at all. Be sure to winterize properly in cold areas.