Here's a couple of questions about career transitions.
1. When changing back to a previous held career, it always costs 1 advance. Does the Reiklander ability to reduce transition cost by 1 apply in this case thereby allowing humans to always transition back for free?
2. Can you transition to a previously held career and not spend any time in it before transitioning again just to take advantage of trait compatibility?
3. Can you transition back to a previously completed career?
So here's the hypothetical scenario. Player starts as a human Boatman ( Basic, Menial, Rural, Urban ) and after a few games switches to Gambler ( Basic, Rogue, Social, Urban ). With two traits in common and the Reiklander ability, it costs 1 advance. So far, so good. After a session or two the player decides to switch to Bounty Hunter ( Basic, Combat, Rural, Urban ). Now if he goes straight to it from Gambler, this will cost 1 advance. If he can go back to Boatman first however, and use his Reiklander ability to reduce that cost to zero and then immediately transition again from Boatman to Bounty Hunter, he can make the move for zero advances.
Setting aside the GM requiring some in-character explanation for the career moves, mechanically it is possible. Adding in the fact that transitioning from a completed career also reduces the cost by 1 advance and there's even more careers a human can get to for free by first moving back to a completed career.
I'm house ruling that you can't transition back to a previously completed career since it has nothing to offer you outside of access to the career's traits, but that only addresses part of the problem. A house rule requiring a character spend at least one session in a career transitioned to (including previously held careers) prior to being allowed to transition out won't change the transition cost; it will at only delay the character for a session. The only mechanical fix is to house rule that the Reiklander ability doesn't apply to the cost of transitioning back to previously held careers and that this cost of 1 advance is fixed. Otherwise, you're stuck with requiring narrative explanation as your only option to prevent players from choosing optimal (least cost) paths for career transitions. Not that there is anything wrong with that, but we all know how imaginative some players can be when it comes to exploiting an apparent rules loophole. I can see power gamers flitting about to cherry pick skill training and fortune dice on characteristics.