Home buyers will probably not agree, but some Realtors and photographers consider it acceptable practice to doctor a photo by making a lawn look green when it isn't. A large photography company is even advertising a September special of 20% off on "Enhancing Your Listings' Lawn with a Green Grass Upgrade!"
Is that deceptive advertising or simply good marketing?
The question isn't as simple as it appears on the surface. What if a lawn service is coming the next day to re-sod the lawn? What if, as has happened this past summer in Chicago, a normally green lawn has brown patches due to lower-than-normal rainfall? What if a local municipality has temporarily banned lawn watering due to unexpected problems?
You can see differing viewpoints on the issue of doctoring photographs in the comments to a post at Photography for Real Estate, a site that's popular with real estate photographers.