That only really works if you are in a position to negotiate, if they actually value your labor, most jobs are just looking to hire bodies to fill a certain role.

Maybe in your field negotiating a contract is common, but in my field there is not too much wiggle room on how much companies are willing to pay. If one company isn't willing to pay me what I'm worth, I just go to a different company, but that's why it's important that I know the salary range upfront, so I don't waste my time interviewing for a bunch of different jobs, just to find out how much they are willing to pay.