Forget farms, this is even how the supermarket produce section works in Switzerland. You pick your stuff, you weigh it yourself, you choose the right tag (without anyone looking over your shoulder) and then you go to a (nowadays potentially automated) cashier.
Heck, it's how the tax system works as well. Government has no way of knowing how much is actually on your bank account, well at least not officially (gov was probably quite happy about the US breaking our banking secrecy). So everyone is supposed to be responsible enough to fill out their taxes and hand in all the information needed. At the end it all works out fine - turns out you can mostly trust people to be honest and the system keeps working for everyone, at least it did so for the last 170 or so years.
Heck, it's how the tax system works as well. Government has no way of knowing how much is actually on your bank account, well at least not officially (gov was probably quite happy about the US breaking our banking secrecy). So everyone is supposed to be responsible enough to fill out their taxes and hand in all the information needed. At the end it all works out fine - turns out you can mostly trust people to be honest and the system keeps working for everyone, at least it did so for the last 170 or so years.