The only difference between a Merit source and someone else is that a Merit source isn't allowed to sell Merit.
Explain that better
Meriting as
a normal user:
You have received a total of 101 merit. This is what determines your forum rank. You typically cannot lose this merit. You have 1 sendable merit (sMerit) which you can send to other people. There is no point in hoarding sMerit; keeping it yourself does not benefit you, and we reserve the right to decay unused sMerit in the future.
Meriting as a Merit source:
You have received a total of 16249 merit. This is what determines your forum rank. You typically cannot lose this merit. You have xxxx sendable merit (sMerit) which you can send to other people. There is no point in hoarding sMerit; keeping it yourself does not benefit you, and we reserve the right to decay unused sMerit in the future.
You are a merit source. The next 123 merit you spend will come from your source rather than your sMerit balance. Merit spent from your source will come back in 30 days. Unused source merit is wasted. It is not allowed for merit sources to sell their merit.
because it infers that those of us who are not merit sources are allowed to sell merit and I doubt very much that you mean that.
It's the same as selling accounts: it's not forbidden, so it's allowed. There are no consequences from the forum, but it's heavily frowned upon. You won't get banned and your sent Merit won't be reverted, but you can get negative feedback from anyone who thinks you deserve it.
theymos talked about how he only saw it as legitimate to red tag someone for selling merit (not for exchanging it, for example, or giving it in a careless way), with no distinction between whether the person selling it is a merit source or not.
Theymos was talking to a Merit source when he said that:
If a DT member tags you for something stupid involving merit (ie. probably anything less than selling merit), then they're not going to be a DT member for much longer.