You weren't just discussing in-game rule-breaking; you were breaking the rules yourself and encouraging other players to break the rules so you could reap a profit on illegitimate business. Account sharing and account-selling is against the rules, and you should know this.
From the ToU, Code of Conduct...
viii. Participating in any action which, in the sole and exclusive judgment of Riot Games, defrauds any other user of the Game, including by scamming or social engineering;
xiii. Playing on another person’s account to “boost” that account’s status or rank; or
xiv. Inducing or encouraging others to violate this Code of Conduct or the terms of this Agreement.
And, yes, I'd consider it scamming; you're having people pay money for accounts on a free-to-play game, and doubtless you had to have played those accounts yourself in some capacity before selling them off to someone.
From the Summoner's Code...
Keep your account information private.
Sharing your account information with a friend can cause your account to be stolen for good or draw a ban for negative behaviour you didn’t commit. Logging into third-party sites with your League account information also exposes you to risk of account theft.
While that particular guideline more refers to personal account safety, there's also the unspoken implication that sharing an account (which poses a great enough risk to you already) would warrant a punishment, which goes hand-in-hand with article XIII of the Code of Conduct.
And, of course, snippets from the Boards Universal Rules.
Account, Product, or Service Promotion.
No advertising product sales, trading, reward programs, or gifting of any kind. No advertising transactional services offered by individuals or companies.
Phishing or Scamming.
Do not post content related to free RP or phishing sites.
Advocating Violations of the Rules.
Do not post content advocating or soliciting violations of the Terms of Use, Summoner’s Code, or Board Rules. Players encouraging this sort of behavior will be punished as if they had engaged in it themselves.
And, yes, while the "Phishing or Scamming" rule explicitly states "free RP" scams, I personally can't count selling accounts in a F2P game as anything but a scam.