Rentals, agents and fees, what’s legal and what’s not

Hi there folks, we are looking to rent and certain people and agencies seem to play fast and loose with unsuspecting tenants, by asking for x months deposit and then a fee for the agent “finding” a suitable property. Can anyone who actually knows this type of scenario, shed any light on what we as tenants would expect to be charged for this type of service? Many thanks.

Agent fees are paid by Landlords on Long Term rentals by law