Under the rules, brought in on 1 April as part of the Charities Act, fundraisers employed directly by a charity must say they are paid and agency fundraisers must also say how much.
Mick Aldridge, chief executive of the PFRA, said the mystery shoppers would operate from May.
The PRFA will also issue a summary of the rules to complement guidance planned by the Office of the Third Sector. Aldridge said fundraisers should tell potential donors as much as possible. "It can help them make informed decisions," he said. "It could be confusing if one fundraiser gives them all this information and another says nothing."