people aren't offering advice, they're simply giving an opinion. It's likely to be ill informed, but that's the nature of a football forum is it not?
It's the same as people giving an opinion on a player, even when they've never played professionally before.
It would be different if they were contacting the club directly and trying to tell them what to do, then you'd expect the person would have some sort of experience to know what they are talking about before doing so.