I can tell you have no experience with negotiations since you don’t understand that all negotiated situations are not the same, and not all call for the same tactics. The approach is different based on strength of position, desire to make a deal, willingness to walk away from a deal etc. he apparently desperately wanted to make a deal with Dallas, and Dallas, as we now know, was not desperate to make a deal, so Dez did not have a strong position, and a hard line tactic would be a poor choice. And the fact is, he wouldn’t have had to say he was willing to take a pay cut up front, but neither did he have to say hell no up front either. The smart thing would have been to not take a stand at all through the media at all.
Frankly I doubt it was a negotiation tactic anyway. Dez has pretty well shown himself to be prone to emotional reaction, and that’s what I expect his hard line comment was.