The property managers I deal with requires $500 or equal to one month rent (fully refundable if not approved) as security when my clients file an application for rentals. Once they are approved I setup a date for lease signing. That's when my clients present checks for Rent, Security Deposit ( remaining balance from the security deposit which they have already given while filing application) and broker's fee. Not before they sign their lease.
You have a right to see the lease in advance and have an attorney look it over for you.
A broker is not entitled to the broker fee until leases are signed by both parties.