How do you offer safety advice when climbing?
You're out climbing at the local crag. You see another person (not your partner) doing something that's potentially dangerous.
Do you speak up?
If you don't speak up and somebody got hurt or worse, how would you feel?
If you do speak up, how do you do so in a respectful and constructive way?
What's your personal responsibility?
Have you ever been on the receiving end of advice about your technique? (I have!) How did you feel about that?
Have you been on either side of this delicate situation?
There are many factors and it's a personal judgment. There’s a big difference between someone using a technique that isn’t ideal or to your liking, and someone doing something genuinely unsafe.
I once came across an anchor that another climbing party had set up with a sewn pocket daisy chain. Not a PAS style with sewn loops, rated to 22+ kN, but one made for aid climbing, with sewn pockets that are rated around 2-4 kN. It was a top rope, where the loads were going to be low.
Is this standard practice? Absolutely not!
Were these climbers in imminent danger of the anchor failing under top rope loads? No.
It was a really goofy way to set up an anchor, but there wasn't anything lethally wrong with it. I chose not to say anything.
What about actions that may have more serious consequences?
Some examples where I have intervened:
Someone about to rappel off the end of the rope
Using a rope too short when top roping, and about to drop the person they were lowering
Here's the general approach that I used in these cases that led to a (mostly) constructive conversation and a good outcome. Your mileage may vary.
Want to know my “opening line” to offer advice?
How about what to say if they don’t want to hear it?