There's an idea which occurred to me for a character. Not so much a PC (it'd be a dull and lonely life, albeit profitable), but as an interesting idea for an NPC who would be a useful resource and an example of a coherent, living breathing world. I wanted to run it past the scholars assembled on this board to see what people thought of it.
I'm thinking of the concept of a travelling Rego Vim specialist with Mercurian Magic, who puts up people's Aegis better than they can, and for a low enough vis cost to turn a handsome profit. The benefits of specialisation in this regard are high enough that it seems wasteful to do it as a cottage industry, with each covenant having their own Aegis caster, especially given the rarity of Mercurian Magic in PCs and the expense of reinventing the Aegis every time for each caster. The only real problem seems to be security-related: The contractor themself will, unavoidably, be able to gain entrance to any covenant where they've worked, and thus will have to be of unimpeachable reputation.
Suppose that you contracted them to cast a level 60 Aegis. Normally this would cost you twelve pawns. Instead, it costs them six. They charge you eight, which is as much as the level 40 Aegis you used to have. You've therefore lost no vis and have an Aegis 20 levels higher, and they've made two pawns profit. That may seem a slender profit margin, but it's not taken them long to do. A single contractor could spend a single season yearly doing (easily) the best part of a covenant. Ten covenants (easily achievable in 91 days) will give them a profit of 20 pawns, which is not bad for a single season's work - it certainly beats distilling vis.
Additionally, there's the matter of inventing the spell. For most people, it's a one off. You buy a lab script, possibly reinvent it to get it the way you want it, and that's just a one-off sunk cost. It's a headache; an administrative expense that nobody wants to do. And every time you want a different Aegis (perhaps you're a growing Spring covenant, or perhaps your Winter covenant can't afford the old extravagance and needs to scale back) you need to go through it again. Having a single person who does this many times, rather than many people doing it once each, is far more profitable for everyone concerned.
It goes without saying that if such a contractor was publicly found to have Harnessed Magic, their business would dry up in a heartbeat.
a) Would your covenant be willing to contract such a service out? Assume that you can do background checks on the contractor in question and that they genuinely are of unimpeachable character, have testimonials from half the covenants in the tribunal, et cetera.
b) What safeguards would your covenant want to put into place, if any? What contractual stipulations would you insist upon?
c) What other things would such a contractor do? If they spend a season a year travelling and casting Aegis, then that means they have three seasons left and a big sack of vis. If that was your situation, what would you do?
d) What other abilities / virtues / flaws / Mysteries / etc would work well for such a contractor? Remember that this is a specialist: standing head and shoulders above anyone else's skills isn't cheesy, it's to be expected from a specialist in a specialised economy.
e) What sort of person, personality-wise, would choose this lifestyle? Would they be motivated by the profit margin? By the opportunity for travel and meeting new people? By simple love of Rego Corpus and Notatus's great invention? What would they be giving up, choosing this path over the normal magus one?
Food for thought. I'd be interested in your responses.