I would like to add that they have taken money from my account twice merely on my sending an inquiry to the host! And I cannot find out how to contact them to tell them so.

No, you can't be sure - I'm sorry, but anyone telling you that you CAN be sure should read all the Airbnb Terms and Conditions before giving that advice. Airbnb say this in their Ts & Cs:

“AIRBNB CANNOT AND DOES NOT CONTROL THE CONTENT CONTAINED IN ANY LISTINGS AND THE CONDITION, LEGALITY OR SUITABILITY OF ANY ACCOMMODATIONS. AIRBNB IS NOT RESPONSIBLE FOR AND DISCLAIMS ANY AND ALL LIABILITY RELATED TO ANY AND ALL LISTINGS AND ACCOMMODATIONS. ACCORDINGLY, ANY BOOKINGS WILL BE MADE AT THE GUEST’S OWN RISK.”

Airbnb may decide to help you out if you have a problem with a host or a property, but basically they can legally wash their hands of it if they want to. You are accepting that fact when you tick the box to say you agree to their Terms and Conditions – which, like most sales websites, is a pre-requisite for making a booking.

One of the most common complaints about Airbnb on the internet is the host cancelling at the last minute. Thousands and thousands of people have great experiences with great hosts - but technically there is nothing in the rules to stop a host doing this. And it's a higher risk than booking a hotel.

So as others have said, you have to take that risk into account. I’d say if you’re booking for an important event such as a holiday, a wedding, a family reunion, etc, have a back-up plan in place or use a hotel.

The main rules for maximising the chance of a good Airbnb experience are:

1. Read all the policies and Ts&Cs on the Airbnb site before you start and be sure you understand them clearly.
2. Don’t book a property or use the ‘Request to Book’ button on the property listing until you have communicated directly with the host via the ‘Contact Host’ link on the listing. (A lot of people make the mistake of thinking that using the ‘Request to Book’ button is just an initial enquiry, but if the host accepts your request to book, Airbnb will take the money from your account at that point.) Ask the host any relevant questions and make sure you’re satisfied with the answers BEFORE you book.
3. Check the host’s cancellation policy especially carefully before you book. The host determines the cancellation period (ie, the period in which you, not the host, can cancel or alter your booking without being charged), not Airbnb. Some of the stricter host cancellation policies mean that if you change your plans or need to cancel, even if you do it weeks or months in advance, you lose a high proportion of your money.
4. In general, just be a savvy consumer and don’t get too carried away by the concept of the “sharing economy” that Airbnb pushes. It’s an advertising platform and a business at the end of the day, it’s not necessarily your friend, much as their PR message would like to make you believe.

How you be sure about anything in life?
What is guaranteed is that you have contracted out a certain time frame, with a certain space. The place is prepaid, just like when a hotel is prepaid thru a booking service. So best way to ensure you will have a place is to talk with the landlord and make sure you have all the directions/instructions. I suggest e-mail because that is a nice permanent record of the communication that you can have a hardcopy with you or accessible by mobile.
Of course, this assumes you did due diligence with looking at the landlord & their reviews, even contacting references as need be, & have all important questions answered before booking. Every time I have done this, I have not been disappointed & I have used Airbnb 5 times, each time in a different location in 3 different towns. May I suggest that chances of a good outcome depend on how much effort you use to find & secure a place. BTW, many landlords have contingency plans if they cannot be there physically to give you the keys - that happened twice to me with NO issues because I talked or txt them about it ahead of time.

Yes, you can be sure that it will be there. Airbnb charges you during booking and ho; ld your money, the hosts only get paid the next day after your check-in.