Found a coin (US dime) unde the floor which the householder was happy for me to keep. Later sold it for $400 on ebay US (rare mark)
Same street years later (last year in fact) found a large grotty envelope underfloor marked '2004 - £15,000 cash'... Have you seen my new motorbike?
Not really, obviously I gave it to the customer - who then confessed he'd forgotten it was there!!