Though I agree with the negatives posted here, I would disagree that all rentals are not good deals. Some rental agencies and individuals "do" run the rig into the ground to get as much profit as they can prior to selling.
OTOH, other rental agencies and dealers that rent take much better car of a rig than some private owners. I rented my rig out thru an agency in Sacramento in the late 90's. There was no doubt in my mind that they took at least as good care of the rig than I could. Here's some things to look for when considering purchasing a rental:
o Maintenance History: Ask to see the rentals maintenance records. For example, make sure the oil has been changed as specified in the owners manual, and so forth.
o Extras Removed: A good rental agency will take the awning, ladder, and hub caps off. They will also lock the hitch so nothing can be towed, remove the coffee maker and cigarette lighter plus place a No Smoking sign on the dash.
o Return from rental maintenance: Ask to see a unit that has just returned from a rental and see the check list and clean up they do.
o Note the mileage cut off for sale: A good rental agency will not keep a unit for more than 2 years, or 20-30k miles before taking them off the fleet and up for sale.
o Who owns the rentals: A lot of rental agencies use rigs that are owned by individuals. It is a great way to get into a newer rig while letting someone else make the payments for the first two years. Most will also allow the actual owner to take the rig out for X numbers of days during the rental period.
So if looking at a rental, ask if it is owned by a private party. A part of what makes this attractive to a buyer of a new rig placed in the rental fleet is that they have approved just how the rig is going to be taken care of. After two years or having reached the mileage cap, the owners have the choice of taking the rig out of rental, or, if it appears they are doing well with their portion of the rental income, can have the agency sell it, and replace it with another new unit.
Most of the rigs in the rental fleet that I worked with were owned by individuals.