Thats not totally right. Turnover can be anything, if expenses are high. Also, the logic you have used is incorrect.
We are haggling over £11m of a £80m deal which is 14%
If you buy a 250,000 house on a mortgage, haggling over £35,000 is actually worth it.
If you are buying a 30,000 car, 14% is 4,200, again I would haggle over £4,200.
Who said there is an inability to negotiate other deals?
If you are buying a house, you will look at other components of the house whilst buying the house but you wouldn't buy without knowing you will be getting the house.