When do you sign your final papers?

Are you having any alterations made to the rig? Are you having any options or features added? Is this a unit that is in stock or are they having to have it brought in? If any of that has to happen before you take delivery, it would be reasonable for the dealer to be assured you are going to go through with the purchase. Even the process to make the rig ready for delivery costs the dealer money they will never re-coup if you walk away at the last minute. A full cleaning, washing, and removing protective coverings costs a dealer several hours of employee time and if you don't buy it, they will have a rig that 1) doesn't look quite as new since all that protective plastic covering has been removed and 2) will have to be cleaned again since birds, wind, rain, snow and the next 100 tire kickers won't respect the cleaning that has already been done.
Also, unless you have fully reviewed and agreed to all the terms in the contract, you haven't bought anything anyway.