A real estate broker within the meaning of this Act is any person, firm, partnership, copartnership, association or corporation, who for a compensation or valuable consideration sells or offers for sale, buys or offers to buy, or negotiates the purchase or sale or exchange of real estate, or who leases or offers to lease, or rents or offers for rent, any real estate or the improvements thereon for others, as a whole or partial vocation. Down Payment The amount of money to be paid by the purchaser to the seller upon the signing of the agreement of sale. The agreement of sale will refer to the down payment amount and will acknowledge receipt of the down payment. Down payment is the difference between the sales price and maximum mortgage amount. The down payment may not be refundable if the purchaser fails.