Yeah, it is usual for us to be more wary after an experience of disappointment. There is this saying: once bitten, twice shy.
Only my close friends, with whom we hang out together most of the time, can be brutally honest, and I won't feel all that bad because I know it's the truth. But when it comes from someone who I don't know, it feels like the person is trashing me or kind of have a beef with me.
Truths that come from those we don't count as valid are usually unwelcome as you say. It doesn't make it any less the truth I guess though. Still, unsolicited advice, observations and opinions are mostly not that welcome I guess, especially if they don't align with one's own thoughts.