It's very common to receive requests from clients to remove or completely change the backgrounds when I'm retouching their images. Sometimes they inform me in advance but oftentimes requests like this come in spur-of-the-moment once the client is happy but then seeks more value to make use of their images. Removing backgrounds is usually the easy part. It's pretty much Photo Editing 101 for any retoucher with any experience. But it becomes a different story when you try to match a background that looks realistic. This is the point where photo retouchers start to earn their money. This is basically compositing, where you must consider the light, color, exposure values, shadows, and any number of other elements that may make the subject or the background conflict with one another if not handled properly.