The Economics of Economical Rice

I’m always quite curious, how does ‘economical rice’ (or more commonly known as,
‘zhup cai png’) stall operators do their accounting?

Considering that each dish is not necessary given out in a standardised portion,
how does he know whether or not his staff are putting the money into their own

Whenever I buy from these stalls, I do not see any kind of action to account for
number the packets sold and the content that’s been sold.

Its a serious question.