New tenants sign lease, then their house fails to sell.

[Kay March]

A couple who was selling their house applied for my rental. They were sure that their house would close on a certain date post lease-signing, and upon my urging (twice) they confirmed with their real estate agent that their buyer's financing was secure. They moved into my rental, and their buyer's financing fell through. They are not complaining at this point about having to make a mortgage payment and pay rent to me, so perhaps I am more uncomfortable than they are, but how do other landlords deal with this risk, or does it just come with the territory?