I had forgotten about these stories written by Roald Dahl and came across one I hadn’t heard before:-
Arthur and Pamela Beauchamp have some friends, the Snapes, for the weekend. For a jest, they install a microphone in the Snapes’ bedroom. After losing a considerable sum at bridge to their visitors, the Beauchamps listen in and discover that their “friends” have a system for cheating at cards. Now they can cheat too  ….. – I haven’t read this yet, so don’t know what the sinister twist in the tale is!!