A company sales can go wrong for many reasons, how do you differentiate between a legitimate reason to not proceed to the sale and a "last minute backing out"?

A company sales can go wrong for many reasons, how do you differentiate between a legitimate reason to not proceed to the sale and a "last minute backing out"? I assume that's what a LOI (which is all that the founder had) is for: it comes before any legally binding agreements and allows both parties to be sure they get what they want without bad surprises.