> Let's say they were price discriminating by looking at the size of your browser window, assuming anything < 600x400 is mobile and charging less. Is it illegal

> Let's say they were price discriminating by looking at the size of your browser window, assuming anything < 600x400 is mobile and charging less. Is it illegal to resize? No. The browser window size, or user agent string are just proxies for the real question: is the device a laptop or a phone/tablet/etc? Your laptop remains a laptop whatever size the window is. This guy's laptop remained very much not a phone after altering his user agent. Edit: It's worth adding that desktop browsers do not use mobile device user agent strings during normal operation, but small windows are perfectly legitimate.