When a real estate agent is selling a house they usually have a contract signed for a period of 3-6 months. Any sale which occurs during this time they get their money. If they are the only agent involed they get 100% if two are involved it's split between the two. The reason being is they spend time showing the house, signage, advertising in various publications, etc.
As far as down payments are concerned that all has to do with closing and the lenders requirements. Real estate agents atleast in the US don't get any money unless the house sells. If you drive down the street and saw a house for sale with a realtors sign in the yard and you went and knocked on the door the people are going to refer you to the real estate agent because it's their job and the owners are bound to the contract. Downpayments are generally required by the lender not the real estate agent or the seller. The lender wants some sort of equitable security mostly based on credit.
I'm an ex mortgage broker, a certified home inspector, and practically my entire family either builds, designs, remodels, invests in, or sells real estate.
