Anne Is a Millionaire Who Is Seeking to Buy a Property

Anne is a millionaire who is seeking to buy a property in London. She hires Dustin who acts as a property search consultant. The terms of the contract provide that Dustin will receive a 'search fee' of 1% of the purchase price of any property which Anne signs a binding contract to purchase.
Dustin selects a number of properties already being marketed by estate agents for Anne to view. Anne chooses to purchase Lofty Towers in Kensington. The estate agent for the sale is Wolfton & Co which pays Dustin one-quarter of the commission which it receives for the sale. Expert evidence shows that this payment had no impact upon the sale price to Anne.
In what circumstances will Anne be prevented from claiming that Dustin is a constructive trustee of the additional commission which he has received from Wolfton & Co?

A) Dustin will not be a constructive trustee of the additional commission if the payment of such a commission is common practice in the sector, even though this was not known to Anne.
B) Dustin will not be a constructive trustee of the additional commission because Anne has suffered no loss.
C) Dustin will not be a constructive trustee if he telephoned Anne prior to the sale contract being signed and told her that he might receive a small additional payment from Wolfton & Co, but did not tell her how much this would be.
D) Dustin will not be a constructive trustee if his contract with Anne specified that he might receive a commission from the seller and the commission did not exceed the limits specified in the contract.