On that last point, arguing YOUR value is always best but your boss/HR, however good a friend they are, has a job to do. Save your company money. So they'll try to politically sell you short on what you're worth to them. Heck, I'm thinking of asking for a raise, and suddenly I'm sent to all of these meetings with IT outsourcing companies!
"Please list these areas where we can save you money...#1/ Systems Administrator - Salary" *Laugh*
Knowing what other people in similar positions in the company make can be a bit of a lever. When asked how you know the information, NEVER directly answer. "It came to me eventually," usually works.
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