Green’s Dictionary of Slang

(UK Und.) the robbery of a shop by a pair of thieves, one engaging the shopkeeper in banter, the other committing the robbery.

1839		H. Brandon Dict. of the Flash or Cant Lang. 164/1: Palming – robbing shops in pairs.
1857		J. Archbold Magistrate’s Assistant 445: Robbing in shops by two – Palming.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn) 185: Palming robbing shops by pairs ― one bargaining with apparent intent to purchase, whilst the other thief watches his opportunity to steal.
1873		Sl. Dict.
1882		Sydney Sl. Dict. (2 edn) 6: Palming - Robbing in shops by pairs, one bargaining, the other stealing.
1880		W. Hooe Sharping London 35: Palming, sleight of hand.
1895		C. Crowe Aus. Sl. Dict. 55: Palming, robbing generally carried out by two thieves, one of whom so engages the victim that he does not feel himself robbed till the thieves are gone.
1935		R.T. Hopkins Life and Death at the Old Bailey 63: The following crook’s words and phrases date from the days of the old Old Bailey: [...] robbing shops by pairs, one bargaining while the other steals – palming.