I think some people who are half thinking of moving put their home on the market to ‘test the market’; knew someone a few streets over that did that. Saw her house on Myhome and when I asked her she said; she was seeing what she could get for it but didn’t want the sign outside her house… Estate agents must be wise to this now - waste of time for them
Another reason could be siblings / friends who bought together and now one wants to buy another the other out. Might feel the only way to get a true value on the property is to put it on the market.
This doesn’t really explain the 3 times sale agreed but apart from advertising costs - nothing is set in stone until contracts are signed