Answer:
The agent has breached Fiduciary Duty
Step-by-step explanation:
Fiduciary duties are in place for estate agent to protect the interests of the seller.
For example if the seller has a higher bid price for the property, the estate agent should sell the property at the higher rate. This is his duty to protect the seller's interest.
In this case, the estate agent bought the property at a lower price and sold it at the higher market value, thus breaching his fiduciary duties.