Many (most?) home sale contracts should have wording to specifically include fixtures ceiling fans etc when buying a house.
As a seller, if you intend to take your fans, lights, etc with you - either make sure that is explicitly understood to everyone viewing the house, (especially your realtor and the buyer's realtor) or save yourself a lot of hassle and remove/replace fixtures BEFORE you start showing the home to potential buyers. If it is just one or two things, it's not a big deal, just state it explicitly. But if you have 8 $400 ceiling fans that you plan on taking with you, you should definitely replace those before showing - or expect to end up throwing them in to close a deal. (who wants to buy a house and then immediately have to go buy 8 ceiling fans)
Most home sale contracts are for "as shown" properties... if the new buyer moves in and those things are missing, you've violated the contract.