So it probably means that a school is OK if I cant find any negatives reviews about a school on the internet?

Not quite. The advertisement from the school can also tell you quite a lot.

The salary level, expected hours, visa type etc. Does the school try to show off its educational prowess or its 'cute kids?'

Does it use words in the school's name like 'Oxford', 'Cambridge', 'Harvard', 'American', 'Canada', 'Eton' etc.? Then it probably has nothing to do with the said institution or country.

We often catch out bullshit positive reviews on here through such methods, a fake review never tends to discuss a school's educational qualities, just supposedly high pay, low working hours etc. Things that wouldn't be at the top of the list for anybody that cares about education at all.