Whenever I type in custom values for salary or various fees and hit submit it automatically raises them to one of its preset values. Yet the preset values often have too wide of gap between them so you're either offering way too much or not even close to reasonable amounts. How do you get the manual values to stick?

How do I know whether my values will stick, so I don't get screwed when I type in 50k and it jumps to 57k?

There are minimum offers you can make for some negotiations . Anything below that gets ignored.

Yeah sadly it's down to board restrictions. Usually you can't offer more than 10% of your team total salary value for a single player's salary, for example.