How not to practice law: represent buyer and seller in a transaction, then represent one of them against the other after transaction is done

Here is a link to a decision from New Jersey imposing a light sanction on an attorney who represented the buyer and seller in the transaction without full disclosure and a written waiver of the conflict and who then represented the seller in litigation brought by the buyer.  This are two obvious violations of the rules it makes me wonder why the court does not challenge the lawyer's competence.  The case is another one of those that can be used to illustrate the difficulty of determining what should be the proper sanction.