I climb a lot of dead trees with no good TIP as most of the trees in town have already been burned and removed. I have the luxury of a very experienced mentor, and he has never been wrong. The few trees he was cautious with did end up being super rotten inside, so when he says it's good, I trust him. You get used to certain wobbles, and when you feel it get a bit too punky under your spurs, check it with your hand saw. If you climb slowly and be very gentle with your flipline, you can keep going. Climb high and cut small. A few months ago, I finally got one that had been dead long enough to have almost no branches left. The sapwood had started to rot a bit, but the heart was all there. Ponderosa pine. At the end of the day though, I don't think I would have climbed almost any of them without 65 years of cumulative experience stand next to the trees in question, telling me that that particular tree will be fine, and the two times I backed out, they got up there and did it exactly how they asked me to do it.