Pulls a fast one on riverside banks (6)
I believe the answer is:
bluffs
'banks' is the definition.
(bluff is a kind of bank)
I don't understand how the rest of the clue works.
(Other definitions for bluffs that I've seen before include "Attempts a deception as in poker" , "Frightens off someone by pretending to be stronger than you are" , "Pretends the cards are better than they are" , "Pretends to have a good hand in poker" , "Tries to deceive as in poker game" .)