as a business owner/operator involved in everything from sales to hiring to vendor purchasing, here's the most important thing: if you can't walk away from a negotiation, it's not really a negotiation. if you feel, at any point, compelled to stay even though your interests are not being met in a reasonable matter, you're going to get screwed - and it's your fault, not the other person's. in a true negotiation both pa…
For me it boils down to this : I try to be as comfortable walking away as I would be accepting an offer. Otherwise I just don't enter any negotiation phase. Also when expressing salary expectations, I try to aim high enough to be sure they will not accept my initial demand. If they did that'd be a sign I just left something on the table.
However, it can be most difficult to put oneself in a position to leave the table. Developers are in a very privileged position in this regard. For most employees walking away could mean being out of a job for several months and employers know this.