The oaths that the "librarii" or booksellers had to swear to the universities to obey their regulations and requirements for the tax exemption were extremely restrictive in regard to the resale of secondhand books. They were supposed to act more like intermediaries between the seller and the buyer while their profit was limited to essentially four pence per pound. They were further required to display the secondhand books prominently in their shops, give a professional assessment of the likely price of the books submitted to them, and put would-be buyers in direct contact with the seller.