Ah! Bob, customer skills and service, something that many have never been taught or conveniently forgotten.
As far as old coins are concerned the most frequent I have ever come across were 100 pesetas coins. which when the new £1 coin was introduced were easily slipped into unsuspecting folks' change.
The new 'plastic' notes are, as far as I can seen, not appreciated by many shopkeepers, post office clerks etc.. For a start they are too slippery, they are far less easily counted when more than four are together and worse still is that when very new can be difficult to separate. Many seem to have fallen foul of handing over, inadvertently, two notes instead of one. This is usually spotted by the recipient but I am sure there are many less scrupulous people around that keep 'schtum'.