In his latest post, Larry Hryb (aka Major Nelson) discussed how scammers can buy stuff on your expense and how complaining would get the victim banned.
"If you run into that person in Halo 3 who claims if they could have your LIVE ID name and password to recover your Xbox LIVE account to their Xbox and they'll rank you up or find you all the hidden skulls in Halo 3, I urge you not to fall to temptation", said Major Nelson. "While it may be appealing, in addition to violating the Xbox LIVE Terms of Use it can also result in you permanently losing your account."
"If that 'friend' of yours decides not return your account and buys a bunch of Arcade titles and movies on your account, there is nothing we can do except cancel the account since you willingly shared your information."
"Cancelled.
As in you can never get it back."
"In addition to losing your Gamertag, you'll also lose your Gamerscore, saved games and any points you have on the account."
In the same post, Major Nelson also revealed that Xbox Live will detect tampered save game files and warned that " If you use tampered gamesaves to boost your Achievements and Gamerscore, you may sign in to Xbox LIVE one day and discover that we have removed your Gamerscore. Once we do that, you will never be able to re-earn those achievements on that account. Even worse, you might have your account and/or console banned from Xbox Live."