Interpositioning: Interpositioning involves a 2-step process that allows the brokerage firm to generate a profit for the brokerage firm from the spread between two opposite trades. Interpositioning can take various forms. In one form, the broker purchases stock for the brokerage firm's proprietary account from the customer sell order; and then fills the customer buy order by selling from the brokerage firm's proprietary account at a higher price — thus locking in a riskless profit for the brokerage firm's proprietary account. A second form of interpositioning involves the broker selling stock into the customer buy order, and then filling the customer sell order by buying for the brokerage firm's proprietary account at a lower price — again, locking in a riskless profit for the brokerage firm's proprietary account. In both forms of interpositioning, the broker participates on both sides of the trade, thereby capturing the spread between the purchase and sale prices, disadvantaging at least one of the parties to the transaction.