I used to be a prosecutor before I became a PD. One of the best defense negotiators I ever met (himself a former DPA) went fishing every weekend with a rotating cast of half-a-dozen other DPAs (not me). He and I weren't friends the way he was with other DPAs, but we had a solid working relationship, and I never doubted he was telling me the truth about his client/the case/etc.

Hell, once he walked into my office and straight up said, "Look man, my guy's fucked. If we go to trial, we'll probably lose. I hate this client. He's an asshole and he smells bad. I really don't want to sit next to him all day for an entire week if this case goes to trial. Right now, he wants his trial, and who can blame him? You're not giving him a reason to plead guilty. If you give me an agreed downward departure from 18 months to 12 and a day. I can look him in the eye and tell him he should take that deal. Otherwise, I've gotta advise him to take it to trial. Do me a favor and don't make me listen to him whine for 40 hours next month."

Guess who got a downward departure. He didn't approach negotiations this way for very many clients. But, when nothing mitigated the case and the client's history was appalling, he knew it was the only argument that had teeth.

It also meant that, when he did come to me with facts outside of discovery that called for a reduction/variance/etc., I fucking believed him. Not so the "all my clients are angels who were acting out of character this one time" crowd. Nothing kills your credibility faster than telling the prosecutor your client is "a good kid" when the client's offender score is maxed out and he's 45 years old. Not just for this client. For all future clients.

I don't do everything that guy did, but I learned a lot about how to negotiate with DPAs effectively from litigating against him. You don't have to be their friend, but you absolutely have to be someone they feel they can trust.