It's as hard to know whether the person is giving good investment advice as it is to give good investment advice yourself, though. So generally, it's not very helpful.

...doesn't this just reinforce that having family connections matter more? Are you more likely to follow the advice of your family or some stranger? If your family connections have insight and/or inside knowledge of markets, aren't you more likely to accidentally take good advice than the average joe? You're still not immune to bad advice, but you have a higher percentage chance of having higher quality information to act on.