I have seen it time and time again. Photoshop users using the stamp tool like as if they are creosoting a garden fence.
If you want to hide the fact that you have just used the stamp tool to restore a part of an image, then please keep your source material fresh.
You should be tapping that Alt key to oblivion! Change the direction that you take your source pixels from every second or so. By doing this you will ensure a more ‘random’ result, leading the viewer away from the suspicion that your image has been tampered with.