An honor system on ticket-checking can work fine if there's high enough fines for being caught without a ticket. If there's a 1 in 10 chance they'll check your ticket, and the fine on riding without a ticket is at least ten times the cost of a ticket, the government comes out even as long as the cost of enforcing the fines isn't higher than the money saved by not having to hire as many ticket-checkers (or spend as much time waiting at the stop because of not needing to check everyone's ticket).