How do buyers choose between products in perfect competition?

Here is what buyers do in order to choose. The thing that drives all choices is consumer’s interest in the market transaction and this is often reduced to that of gaining the maximum amount of the good in question for the minimum amount of money. It is said that theories support the idea that consumers cannot choose between goods on the basis of quality, since goods are taken to be homogeneous. So they choose by means of how mcuh interest they have in an especific product.