One important lesson I learned on my property journey when I was a Real Estate Agent, was to never trust the sale had been finalised until completion.
Anything can happen between an offer, exchange and completion.
The deal could fall over at any time. For example, the buyer may not be able to raise the funds, the survey may come back as being unsatisfactory or the buyer may simply change his/her mind.
The seller may even change his/her mind. That’s why is always important to follow up and be on top of the process at all times.