Which FINRA rule requires that a member and all associated persons must use reasonable care to find out the best market for a security and buy or sell it so that the customer's price is as favorable as possible?

Explanations

FINRA Rule 5310 requires that, in any transaction for or with a customer, a member and all associated persons must use reasonable care to find out the best market for a security and buy or sell the security so that the price to the customer is as favorable as possible.