I think it's cos we tend to assume that if someone gives one good bit of advice and that's what you come across first then you tend to assume the rest is prob legit too.

It's a bit like first impressions. The laziest man I ever met in my entire working life told me that the first time he goes to a new setting (I was working in care at the time) he finds and does the dirtiest, toughest job he can find there, the kinda job everyone avoids cos it's just really shit - giving the oven a good clean for instance or deep cleaning the laundry room. It doesn't last forever, but he'd coast on that first impression for quite a while.