Here's why honesty can work out...people sometimes can't see what you see so if you really think you can help with a friend's parenting issue (tackle by issue NOT by style, is what I found works)...here's my recent experience:

I have been having trouble with my 8 year old- we had a crazy year and he's emotionally reflecting the chaos.   We moved from Colorado and life is very different. He was in a montessori preschool and eventually montessori public charter school.  He performed awesome at school and he loved the structure that it provided. Well, coming here to public school (because there is NO montessori community :(- )  he fell apart. He went from multi-aged mega-hands-on-high level to single age traditional (he's moved classrooms though, which has helped).  His life funtioned well and he was responsible and very independent. I let him be that way- it worked. But not here, and he has been a mess...

Anyway, my neighbor has a solid, strong, no-BS but loving parenting style. With all these behavior issues popping up (with my son) I asked her for advice... She told me that with all his emotional meltdown, I wasn't drawing a clear enough boundary in certain areas that made him feel safe. I thought I was,  but she pointed out how she handles this stuff and I actually listened (where I might usually get defensive). I knew I needed an objective perspective. She gave me some criticism but in a helpful way.  I appreciated it- even though I felt a little stupid. I took it though, knowing she's not perfect either but in this area, she had it dialed...

Her honesty has helped me shift some of my behaviors- and I'd say I am pretty well in-tune with that stuff. I have a master's in ed. psychology (student learning & behavior) and I STILL needed honest outside perspective to see a more cut and dry way to handle my son! Thankfully, her advise has truly helped and I am seeing change and we all feel a bit better.

Bottom line: if you see an issue and a friend in need, don't hold back, if you really think you can help!