What does "that place is a real bucket shop and they tend to work only with pikers" mean?

A "bucket shop" is an unethical business operation:

A fraudulent brokerage operation in which orders to buy and sell are accepted but no executions take place. Instead, the operators expect to profit when customers close out their positions at a loss.

or:

A brokerage that makes trades on a client's behalf and promises a certain price. The brokerage, however, waits until a different price arises and then makes the trade, keeping the difference as profit.

(Investopedia.com notes that the latter definition "comes from more than 50 years ago, when bucket shops would do trades all day long, throwing the tickets into a bucket. At the end of the day they would decide which accounts to award the winning and losing trades to.")

A "piker" is a small-time player, someone who operates cheaply and takes only small risks in a very cautious manner.

So, Bernie is saying that this place is a shady operation that caters to cheap, chintzy, risk-averse individuals and tries to continuously cheat them out of small amounts of money; they will throw in only an occasional small payoff to a customer to offset a part of the overall loss suffered, so as to keep him hooked on the possibility of getting a big payoff.