The Fife said:
If the grass or house doesn't actually look like the pictures, to me that's false advertising.
There are rules to follow, and it's definitely led to lawsuits in some cases.
If it's a characteristic that changes with weather, time of year, etc., it's acceptable to show it at its best (or what it WOULD look like at its best). The line is drawn at "fixing" things that are wrong with the actual structure or removing undesirable elements altogether. Make the grass green, but don't clean up the landscaping. Add leaves to the trees, but don't remove the power lines. Show the pool nice and blue, but don't fix the cracks in the deck.
Personally, I don't change the grass, other than touching up spots with nicer patches of what's already in the yard. And instead of fixing or removing certain elements, I just show it from a different angle. There are some ethics involved in that too, even without doing any extra editing at all. There's a pretty famous case of someone using a very low angle for the front exterior shot, eliminating from view the power plant that can otherwise easily be seen beyond the rooftop.
For me, the worst part of the photos above is the sky. The grass is much easier to forgive.