It's still a bit of a challenge being a buyer trying to purchase a home; however, if you're a buyer and the home that you want goes under contract, it is a really good idea to ask the listing agent if they will accept a back-up offer.
This happened to us twice in the past month. We listed 2 homes and both homes had buyers that backed out. We immediately went to our back-up offers that we had and got the homes back under contract the same day! One home has since closed (this beautiful home pictured) and the other will here shortly.
Never give up on what you want. It's always a good thing to be waiting if something falls through.