"You might be worried about people monkeying with markers. Fear not, we've thought of that. Whenever you find a recently-moved address or business, you'll see a "Show original" link you can click to see where the marker was originally. If it's in the wrong place, just move it to the right one," explains Google LatLong Blog.
This also works for locations of addresses and landmarks, but only in the US, Australia and New Zealand. More about the new feature here.