Just to clarify, I think we're all saying the same thing, but using the term "good faith" differently. In the Ridgewood, NJ (not sure why Trulia places me in CA!) area, contracts are signed at the time of the Buyer's initial bid, and some sort of earnest money must be included, which is what we commonly refer to as the "good faith" deposit. This is deposited with your real estate firm, and temporarily held until the price negotiation with the Seller is complete. This is different from the total deposit you will put down if a deal is reached, and it's also different than the balance you will put down on the entire transaction.
Let's say you want to purchase a house for $500,000. In the Ridgewood, NJ area, your chances of reaching a deal are best if you are looking for 80% financing or less, and you are able to put down a 10% deposit. So, for example, let's say you submit a contract to the Seller with a $500,000 purchase price, a promise to put 10% ($50,000) down within approximately the next 2 weeks, and another 10% ($50,000) at closing, leaving the 80% balance ($400,000) covered by the mortgage. At the time you sign the contract, you will attach a check (again, usually $1,000) that represents the good faith deposit. Then, when Attorney Review is complete, the balance of your 10% down is due, which is this case is $49,000 since you've already given the smaller check up front. I hope that helps.