1. A method comprising: calculating, by a computer-based system for automatically sorting customers who make purchases from merchants using a transaction account, an adjusted index for a customer based on an amount of money the customer spent across merchants during a time period; comparing, by the computer-based system, the adjusted index to a cut-off value, wherein the cut-off value is indicative of a first category of transaction account users likely to be business users and a second category of transaction account users likely to be consumers, wherein the cut-off value is determined from a manual categorization of transaction account users and wherein the cut-off value is set above the lowest adjusted index of manually categorized business users; classifying, by the computer-based system, the customer as a business user in response to the result of the comparison of the adjusted index being greater than the cut-off value, wherein the classifying occurs without active category selection by the consumer; switching, by the computer-based system, the customer from the second category to the first category, in response to a number of business transactions of the customer with merchants of a particular industry exceeding a threshold within a period, wherein the switching is regardless of the comparison of the adjusted index to the cut-off value; and assessing, by the computer-based system, a comparative risk associated with extending credit to the customer based on the classification.