Our house. Ver naice estate house on ver naice commuter estate in Home Counties. Fully newly refurbished, valued at £575k by 3 agents.
We saw the only house we have said we would move for, and so are selling ONLY for this house. The house is on with agent F, we are selling through their sister company next door, J. (F deal with posher and rural stuff, J is more urban, but they share sales support and are essentially the same company.)
We offer on the house we like. Offer accepted subject to survey - likely to be issues, it's a wreck and has been on the market with F for 16 months...
We put ours on market at £550 to get a quick sale. Accept offer at £537 and encouraged to remove outs from the market as our buyer, MrsM, is also selling through F, and if this chain completes, they get all 3 fees. We agree, so long as the house we are buying, from MrsA, is also removed from sale.
So far so good. But then MrsM takes AGES to sell hers. We ask to go back to active marketing. Our agent agrees but then secretly refuses to allow new viewings on ours, actively dissuading people by saying its "nearly sold."
(Got friends to phone to try and arrange viewings).
Finally get a call today: MrsM has sold but for far less than she was hoping so her offer is now £525, but her buyer is cash, so it's procedable.
I'm fuming. We could have bloody well sold at £525 a dozen times over, weeks ago.
And the agent's fee for this? £6000. 
Pass me a slingshot. I'm going in.