I have just been in my local Tesco store and to my surprise they had Halo 3 on sale. How would xbox see this if bought legitimately and you go online. Could they ban you ? i expect so and who would be to blame. I pointed out to one of the sales people who manage that area that they could have complaints from angry parents from banned xboxes. looking at other sites this may be intentional.
Some video game stores release its games several days or even weeks before the official release date. If you logged onto live before the official date, you got banned.