Copywriting is a skill of writing sales letters. It pays much more than data entry, but it is much more complicated
No one, because I've never read any book written by a copywriter. I've read marketers, but none that were (Or claimed to be) good copywriters. And therefore my perspective is uncluttered. I write copy based on what I know (or think I know) of people and their needs, human psychology and such relevant? stuff.
Probably better to look at their client portfolio pieces instead. Most of the full-time copywriters I know are too busy with client work to get around to updating their own sites. I'm certainly guilty of it.