Value is arbitrary.
Each person assigns the value he wants to whatever item. Of course, there is an international value assigned to gold and brass, and so you could argue the Spaniards took advantage of the naivete of the Taínos. But since brass was the scarce and beautiful metal for the Taínos, they were willing to trade gold for it.
Today, some people value brandname clothes. Others value attending their favorite band’s concert. Others treasure their pets and deprive them of no extravagance. And dumping boatloads of money on it is well worth it.
Some people value their family. Some people value cheating. Some people value faith in God.
Are you trading brass for gold?