There was a push for a gated system here, some years ago. The vendor tried to sell it on massive cost savings...and was publicly humiliated by a bunch of geeks with an Excel table. Turns out, installing and running the gates would, at best, bring parity with random ticket inspections+fines - while impeding passenger flow as a bonus.
It's not necessarily a matter of education: just the feeling of "not worth freeloading (at the price), I'm likely to get caught anyway" is sufficient.
Differentiate nomal daily sales rates within the test day, observe the trend year by year. Sounds naive, would be lovely if it works.