Green’s Dictionary of Slang

loo v.

[? the card-game loo]

(US) to cheat, to defraud.

[US]N.-Y. Eve. Post 19 June 2/1: [heading] Uncle Sam loo’d again. – Never was such luck! such cursed luck! This time the pool was a thumping one: no less, it is said, than three hundred thousand dollars, upon the table.
[US]N.-Y. Eve. Post 6 Dec. 2/5: [The thief] was brought up, and $100 recovered, which [the victim] carried off, highly delighted, he being looed out of the $80.