[Stairs]

You may think your house is worth 100k, but if your best offer is 80k, your house in reality is worth 80k, (whether paid in instalments or any other way).

Your wife asks you to move house and you reluctantly agreed to do it. But only if the valuation of £100k was met.
Subsequently someone agrees to the asking price. That's great and your wife is happy and excited.
But then they actually you £20k up front followed by a series of 4 additional 20k payments over 2 years based on how much they like living there.
You can't buy anywhere else to live for 20k and no-one else is prepared to sell there house on the basis of annual instalments.

So you have to refuse the sale.

Your wife is pissed off with you, her friends who don't know the facts point fingers at you and you are made to look the villain.