Where a general agent, having power to sell a piece of land, limited only in the method of payment, and the agent having control of a building on the land, upon a sale of the land at public auction, announces, in the presence of a tenant, that the purchaser, after a named date, shall be entitled to the rents, and the special agent, upon the payment for a part of the time to the purchaser, expresses approval of it, the principal is estopped from claiming rent paid to such purchaser by such tenant. Knox v. Barnett, 18 Fla. 594.