It is naught, it is naught, saith the buyer: but when he is gone his way, then he boasteth.
It is naught, it is naught (the ware on sale is bad in quality and quantity), saith the buyer. The repetition expresses superlative worthlessness. The buyer says the same thing over and over again.
But when he is gone his way, then he boasteth - of what a clever bargain he has made; what a good thing he has gotten at a cheap price. We must not do as the world commonly does.