I am trying to avoid two possibilities : sources having more unspent smerit or sources doubling rewards to avoid the first case, which i think both aren't good choices. Sources could confirm or "deny" these facts.
Please could you qualify that. Do you mean merit sources with unallocated source merits, or do you mean their earned sMerits that they haven't spent.
As I have said previously, it isn't possible for them to spend sMerits until they have used up all their source merits. Source merits are replaced 30 days after they are awarded, so the system is self-moderating.