Green’s Dictionary of Slang

1. a decoy.

1984

Partridge DSUE (8th edn) 147/2: late C.16.

2. a thief; thus buftrap, a thief-catcher [note Eric Partridge in DU prefers ‘harlot’s protector’, although the rest of the list are all synons. for ‘thief’].

1592		Greene Disputation Betweene a Hee and a Shee Conny-Catcher (1923) 5: They haue their Ruffians to rifle, when they cannot fetch ouer with other cunning, their crosbiters attending vpon them, their foysts, their bufts, their nippes, and such like.
1753		J. Poulter Discoveries (1774) 42: The Buftrap johns me; the Thief-catcher knows me.