Fla. Stat. § 475.43
In all criminal cases, contempt cases, and other cases filed pursuant to this chapter, if a party has sold, leased, or let real estate, the title to which was not in the party when it was offered for sale, lease, or letting, or such party has maintained an office bearing signs that real estate is for sale, lease, or rental thereat, or has advertised real estate for sale, lease, or rental, generally, or describing property, the title to which was not in such party at the time, it shall be a presumption that such party was acting or attempting to act as a real estate broker, and the burden of proof shall be upon him or her to show that he or she was not acting or attempting to act as a broker or sales associate. All contracts, options, or other devices not based upon a substantial consideration, or that are otherwise employed to permit an unlicensed person to sell, lease, or let real estate, the beneficial title to which has not, in good faith, passed to such party for a substantial consideration, are hereby declared void and ineffective in all cases, suits, or proceedings had or taken under this chapter; however, this section shall not apply to irrevocable gifts, to unconditional contracts to purchase, or to options based upon a substantial consideration actually paid and not subject to any agreements to return or right of return reserved.
Fla. Stat. § 475.43