Specifically, for 250 of the 495 U.S. firms listed in the guide, we ascertained the states in which each firm collected sales taxes on online sales. For each firm, we followed the following sequence: First, we visited the firm’s website and searched for a listing of states in which tax was collected; second, if the website data was inconclusive, we contacted the firm’s customer service department; third, if customer service was unable or unwilling to provide the information, we researched the firm’s website, its Securities and Exchange Commission filings, and other public data, for a list of states in which the firm in has a retail store or other physical presence.