I run a set of sims, and this is always on my mind.
I don't ask Real life information because frankly, my customers don't want to give that up, and under Linden Labs TOS, that is a violation. With that contract between me and Linden Labs, I could not require RL information if I wanted to.
monthly I clear the costs of 3 'islands' (295/mo ea) and have to wonder if one day everyone will just poof. I doubt it, but it's a risk I take.
As for the client end (renters) they take the risk of me walking away and canceling my islands, but for their anonymousness, they tolerate that risk.
as one of the other posters said, no those rental contracts I have with them are not 'valid' which is why I simply have a pre-pay agreement with a statement of NO REFUNDS. so if you don't like the terms, don't rent.
My only safety net is to keep a reserve big enough to handle a complete loss of clients just before a billing date. It is just me RP'ing a land-lord, but at least my clients RP paying renters.