Whether you're trading in or buying an Xbox 360 at GameStop, the value hinges on five variables.
The website estimate is a guideline. The final offer comes after a staff member tests the disc drive, boots to dashboard, checks the hard drive, and verifies no console ban. Expect the in-store number to be within 10–20% of the online estimate—sometimes lower if they're overstocked.
Pro tip: Check the website for the latest rates right before you go. They update frequently.