Security for selling MacBook Pro for parts
In my opinion, there is no need for concern. I genuinely believe that it is highly improbable that someone would take the time to retrieve data off an old hard drive. In time old credit card numbers that might be stored will expire. Perhaps you can change the passwords of frequently used websites. Thats a good measure anyway. So essentially the data would be useless. If it has proprietary information that is work related then you may take more caution.