5 yuan commission is the minimum for each transaction. If the commission is 2.5 per 1, your single transaction can only exceed that of 5 yuan if the amount reaches more than 2, yuan. So we can't tell if it's a pit, because every transaction requires a minimum commission from 5 yuan. If the commission is 2.5 per 1, your single transaction can only exceed that of 5 yuan if the amount reaches more than 2, yuan.