One of the words to be expunged from the new edition of the Enid Blyton books (see yesterday's post) is tinker. A tinker is (or was) an itinerant craftsman who mends metal kettles, pans and other household utensils. In Ireland and Scotland tinker was generally the equivalent of gypsy. We can be sure that tinkers were never held in high esteem because of the general tone of (dated) English idioms containing the word: to swear like a tinker, as drunk as a tinker and as quarrelsome as a tinker. In Enid Blyton tinkers are often thieves and scoundrels, and are almost always foreign.
Up until about thirty years ago, tinker was often used when talking to small children eg "You little tinker!", meaning rogue or rascal. I can remember elderly neighbours and relatives saying it. It was used playfully. Beggar was another word that was used in a similar way, eg "what a dirty little beggar you are!".
Johnson's explanation of the origin of the word tinker is "from tink, because their way of proclaiming their trade is to beat a kettle, or because in their work they make a tinkling noise" (the definition of 'tink' is 'to make a sharp, shrill noise'). The OED doubts this, as the word tinker was in use as a surname or trade name a couple of hundred years before the verbs tink or tinkle were first recorded.