1. A computer-implemented method performed by a computer processor of learning characteristics of product variables within web pages of a merchant, the method comprising: receiving a product feed identifying a product offered by the merchant and having a value for a product variable associated with the product, wherein at least one of the product variables is a price product variable stating a price of the product; obtaining a web page of the merchant, the web page being associated with the product; producing, by the computer processor, a model representing the web page, the model having a set of nodes representing portions of data of the web page, wherein at least one of the nodes is a price node; identifying candidate nodes of the model that match the product feed value for the product variable; learning, based at least in part on the candidate nodes, product variable characteristics expected of a node representing the product variable; and storing the learned product variable characteristics.