Without conclusive evidence I believe it's critical to give the benefit of the doubt to rezwalker to prevent abuse down the line due to any loosely-given negatives for an A->B transaction to the receiving end. If we start tagging users who receive merit from an untrusted source then it arms negatively-trusted users with the power to ruin some accounts. If then, there are exceptions, then those same users will now be able to obfuscate and dilute their actual merit abuse.
TL;DR: don't create an abusable precedent, no tag.