But a mystery shopper exercise carried out by 5 live Investigates found that some letting agents were still charging fees.

BBC: Call to clamp down on unscrupulous letting agents

If loose lips sink ships, a too-revealing mystery shopper could certainly submerge an hotelier or two.

CNN: Confessions of a hotel mystery shopper

But like a CIA agent or the rare hair stylist who'll keep your secrets, gossip is not in the mystery shopper's after-hours repertoire.

CNN: Confessions of a hotel mystery shopper