I'm somewhat of a Monster renter and I can only answer from my perspective. As the Owner, I insist on a signed contract from my renter for our mutual protection. It specifies what is and isn't included (like daily housekeeping), that the Rentee is responsible for all damages and debts incurred to the room, etc. It also explains cancellation/change policies, payment due dates and the like. This way, I don't forget to inform a new renter of something important, and a renter has many of their questions answered.
In the real world, the cost of enforcing the contract is probably too prohibitive to be of any value, but at least clear lines of communications are opened.
I, again personally, don't take offense when referrences are asked for. It happens about 5-10% of the time. I'm also not offended when a renter expresses concerns about the posibility of them getting ripped off, this is the internet after all, and many of my reservations are in the many thousand dollar range. Like Diane, I'm an honest bloke (although, you have no way of knowing that) and I'll bend over backwards to make you comfortable. It is your money that I'm trying to earn!
Having said that, I have had several renters who gave me a 'squirely' feeling, and I broke off dealing with them (before money or a contract changed hands). If you're not comfortable with me, or I'm not comfortable with you, then there are plenty more Owners and Renters out there, no need for us to 'torture' ourselves.
Now, I find many of my prior renters coming back to re-rent, and I prefer this, since we are both known quantities. I give them a price break, and they don't need as much hand-holding the second or third time.
I have no scientific or hard evidence, but from this and other Disney boards, it seems that there are more 'bad' Renters than Owners out there.
I'm sure if someone had a bad experience or got ripped off, that they could post it here publically, without naming any names (as that would be an attack and against posting guidelines).
Have a great vacation!
-Tony