Saying, 'When will the new moon be gone, that we may sell grain? And the Sabbath, that we may market wheat, Making the ephah small, and the shekel large, And dealing falsely with balances of deceit;
"And the shekel great ..." Coinage was unknown until a later period; and weights were used for weighing the amount of silver, or other substance, used as the medium of exchange.  Of course, if a dishonest tradesman used one set of weights for buying, and another set of weights for selling (neither of them being true), he would be able easily to defraud his customers.  A similar deceit was used with regard to the ephah, a fact demonstrated by the truth that, until this day, nobody knows for sure what an ephah was!  They were indeed a vicious class of robbers, exactly like those that Jesus ran out of the temple during his ministry.