The OP started out with a discussion about a cashier not knowing the difference between say, zucchini and cucumbers.

Aren't there some possibilities here when self checkout is used?

For example, if one produce item costs 60 cents per pound, and another costs $4.00 per pound, suppose a poor flustered confused consumer presses the wrong button and ends up buying the $4.00 item for 60 cents? Because even professional cashiers are easily confused by the multitude of produce items, I can see how it would be reasonable for an ordinary consumer to also be confused.

There would appear to be no enforcement mechanism here because the only "check" is the weight of the item...and of course a pound of feathers has the same weight as a pound of lead.