karrensmt:


... A typical trick in less reputable establishments
is, if you pay with a note, to give you change as if you tendered a
note of one denomination smaller. For instance to give you change for
50 euros if you give them a 100 euro note, and then pretend it was a
mistake if you notice. The best way to avoid this happening is to
speak the value of the note as you hand it over, "100 euros", so they
can't claim not to have noticed ......

They can't??

They can still claim they hadn't noticed.
They can claim to have 'overheard' you saying so
They can claim the missing 50 euro bill is for "tourist taxes".
They can claim they gave you proper change, and you made the missing
note disappear.
They can claim that they will handle your objection tomorrow, because
they're closed now.