Grand Theft Auto: San Andreas is officially the most oversold game of all time. There is no disputing this.
The game isn't even the best in the series yet the games sales were inflated significantly as a result of numerous controversies which made the game extra popular (most notably the hidden sex mini game in Hot Coffee in earlier versions of the game) in the eyes of consumers that wanted simulated crime/sexual experiences without actually committing any acts of this nature in real life.
Proper order will be restored once New Super Mario Bros Wii surpasses it as the greatest selling home console game of all time not bundled "officially" with a home console or peripheral accessory.