The important thing as a host is to remember to keep your host turned on. If renters cannot verify you still have the files at the end of the contract period (because your machine is turned off), you will not receive the coins! In that case, the coins are refunded to the renter. Oh, and keep your wallet unlocked too!
What if there is a power outage where you live?
Power outages are usually short (hours) and should not be a problem. Persistent downtime each day is a problem.
But, if you have a power outage at the exact time renters check your host for files, you may be out of luck (for just those files, mind you).