What separates awful photoshop jobs from good ones?

I didn't know it was offensive to some. I'm an American and most I know use it when they don't want to use profanity.

When you say time, money, and skill - what would they do differently? Could an expert take any old picture and do that, or is it that the photos are lit in a special way (I notice most have a lot of visible light).

If it is just in photoshop, what are some of the things they do? I know one would be going through each edge - pixel by pixel - to ensure there is no remnant of the old background. What are some other things?