Agree with others...you can do it, but it might not work.
We had accepted an offer on our house about a month ago, and made an appointment to see a house. Before we saw the house, we were told that our buyer couldn't get a mortgage and the sale was off. We liked the new house, made an offer....but were open about the situation.
Reality is that if someone else comes along who is in a position to move quicker than us, the sellers will go with them.