A developer or seller can credit you how ever much money your particular loan program's guidelines will allow. Typically this would be no more than 3% of the purchase price of whatever home you are considering purchasing, but some lenders do allow as much as a 6% credit back to the buyer.
Whether or not a seller's credit can be applied to your down payment is also dependent upon your loan program guidelines. Some lenders require that your down payment funds be "seasoned" meaning that these funds have to have been sitting around in one of your own personal accounts waiting to be used for a certain period of time. Other programs allow seller credits to be used for either down payments or closing cost assistance.
If you do not already have a loan officer or mortgage broker, then you should get one as soon as you're ready to begin the process. Most lenders may be quite busy right now due to the most recent decrease in interest rates, but if you need a referral to a lender let me know and I'd be happy to forward you some names of folks who could assist you.
Christopher Thomas, Broker Associate
Sudler Sotheby's International Realty
1634 E. 53rd St. 2nd Floor Chicago, IL 60615
773-418-0640 (cell) 312-673-8752 (fax)