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For the three years after you receive the FTHBC, the IRS sends you a letter called a Notice CPO3b, Courtesy Message About your First Time Homebuyer Credit. This notice lets you know what to do if you sell the home or it is no longer your main home. Generally, you must repay the entire credit for the year you sell the home or it is no longer your main home. There are some exceptions to this rule, however, and you do not need to repay the FTHBC for a home you purchased in 2009 or 2010 if it remains your main home for the three years after the purchase.
Here is your CPO3a sample notice - http://www.irs.gov/individuals/article/0,,id=227895,00.html Your client will not repay the credit if there is no gain on that sale, but the form 5405 should be filed any way.