Oh for FSM's sake.
Fine. No one is allowed to sell any seals whatsoever except to the Tower, at a rate the Tower decides. You may buy seals from the Tower and not from anyone else. They set whatever rates they damn well please and vary it from person to person on a whim.
The Tower is considered to own 30 hours per week of every sealmaster's time. Every week they specify what you will make for them this week. You either supply it, get someone else to make it for you, beg for an easement, go missing-nin, or deal with ANBU for breaking the law. Everyone who is capable of making seals is required to be licensed. Making seals without a license is treason. Having the capacity to make seals but not getting licensed is treason. Going missing-nin when you are a sealmaster is a "Top priority, bring me his skin and if he's still inside it that would be nice, but don't fuss" sort of thing.
There. It's a vastly more ducked up system and therefore far more appropriate for the screwed-up place that MfD was originally conceived of despite my preferences, so you can all object to the world being craps instead of the economics not being what you think of as perfect.
Grr.
...
...
...We probably shouldn't do this. Still, the simplicity is tempting, and it nicely explains the Tower's source of income and gives them a source of power over the clans. And it's more appropriate for a 12th century military dictatorship. And if we assume that the Tower provides high-end reference materials, labs, and other facilities, that would explain why the sealmasters put up with it. (Aside from "because we're the only game in town and we'll wreck you if you buck the system too much.")
Hm.
@OliWhail ,
@Velorien ? Thoughts?