In the spring we bought a B+ from Canadream and we are very happy with it. I did have the same fears about abuse and unit not being clean but I have to say that everything was clean, they gave us a new mattress still in the plastic and as they do not allow pets and at the cost to rent one of these units, approximately $5000 per week, they do a detailed inspection after each return and provided us with full detailed report as to what was done each time. Finding a B+ at a reasonable price without going to rental locations is very difficult. The unit had low mileage and price was right for us and if we had to do it over again I would certainly consider it.
I know that I have looked at other rental locations and to be honest would not spend 15 minutes in the unit so I guess it all comes down to the rental agency and how well they look after their units. Some wait until their units have lots of miles (100000 plus) but others rotate their inventory more frequently.
Good luck finding your perfect fit.