AirBnb, and the other major rental agencies, have cancellation policies upfront that give you some choice. AirBnb has several levels...one allows you to cancel almost up to the last minute, others have shorter deadlines. An advantage of using an agency that works this way...pretty much like a hotel booking site...is that the intermediary is holding your deposit and that can save hassles.
Obviously, rules about dissatisfaction vary also, but usually if it can't be ironed out, you'll get at least a partial refund, or all if the agency recognizes that what you got was not what was described.
As with most travel arrangement...there are some risks on both sides. The host is counting on income from those days and may not have a customer waiting if it's too close; on your end, the plane, etc.