Green’s Dictionary of Slang

best v.

[orig. dial.]
[late 16C; early 19C+]

1. to get the better of.

2. to cheat.

In derivatives

bested (adj.)

[mid-19C+] defeated, defrauded.

bester (n.)

1. [mid-19C] a villain who is equally happy to use physical force or verbal deceits to extract money from victims.

2. [mid-19C] (UK Und.) a criminal who deceives his peers.

3. [mid-19C+] a fraudulent bookmaker.

4. [late 19C] (Aus.) one who lives by their wits.

In phrases

get money at the best (v.)

[19C] to live as a professional criminal.