There are several rental agreement samples available here on TUG. In the toolbar (on this page). Go to: Advice -> Renting articles. I used TimeshareVon's Generic Rental Agreement and doctored it up a bit with some things I specifically wanted to include (or exclude - like I don't require a signature).
Realistically - I'm pretty certain it would not hold it's weight if I had any issues. Transacting across states, etc, I can't imagine trying to legally pursue anyone. I make it simple, 'by paying the invoice you are agreeing to these terms', so there's no signatures for either of us required. I don't want that hassle. And again, have very low expectations that it would help me out in court anyways.
I'm sure it's scared away a few people I'd prefer not to rent to ("what, i have to count the silverware?"). And if something major did happen, perhaps it would be of some benefit (who knows). I state the details of the transaction in the rental agreement and it's a good reference for me. It's pretty much my booking/records and if I promised anything to someone (a free upgrade, what I will charge for an upgrade, or if I offered a refund if I get a discount, anything I may want to refer to later). The details come in handy for me.
It also allows me to set some expectations. No refunds, what to do when leaving, don't exceed occupancy, no pets, fees that may be incurred, no timeshare presentation required, can't guarantee a view, etc.
I can count on one hand the number of times someone has stayed and hadn't paid before staying (very unusual circumstances, hurricane - already there, need an extra an extra room or someone ill while there and need to stay, those extremely unusual (and emergency type) circumstances).
Maybe on 2 hands, the number of people who don't pay before the 15 day cancellation mark (that would only happen with a last minute rental). I also have my money.
I've had 2 times I think that someone has contested a payment to PayPal (and yes PayPal refunds 1st, asks questions later). Thankfully, in both situations the person forgot my name and didn't recognize the charge when they saw it, so filed a dispute. They were honest mistakes and I got my money. Reality - you would likely lose a dispute with a dishonest person.
The biggest burn for me, was selling last minute on eBay, and the person didn't pay. My hands were tied. I call that being held hostage by eBay feedback. The item was sold and they kept saying they would pay and never did. They didn't use the room, I did not put the guest confirmation on it. But it sat empty. Ebay is not at all helpful in this situation. Yes, they refunded the fee for the ad. I had a room sit empty. I am much more careful with my eBay ads now. I try to make those last minute things buy it now so they have to pay immediately. It's not always easy, if you are accepting offers, you can't make them pay immediately.
I have not, nor ever would, used Wyndham's Extra Holidays. I can't imagine that being profitable the way I understand it is run.