If you don't want to see some minor spoilers, close this thread.
I figured I'd make this thread as a public service announcement, since I didn't actually know about this until I went back to check.
The npc in the Homestead who offers to let you respec also offers three other services. One to increase reputation, one to increase attributes, and one to increase abilities. If you're like me, you ignored the first one and were puzzled by the second two when he said something about 'marks of ability' and 'marks of talent'. What are those. I don't remember finding those.
Long story short, what he actually offers is
-Lose 1 point from any Attribute to gain 1 Reputation
-Lose 5 unspent Ability points to gain 1 Attribute point
-Lose 1 unspent Talent point to gain 10 Ability points
I want to reiterate that last one. You can turn one talent into 10 ability points. Holy crap. By spending all of your talent points this way, you can get a total of 118 Ability points, by level 20. Enough to max out almost 8 Abilities, even before equipment bonuses, without abusing the Seller of Secrets at all. By sacrificing 3 talent points, you gain the ability to completely max out 2 new Abilities.
This is a huge game-changer.
FAIR WARNING
Once you make those trades, the effects are irreversible. Even if you then purchase a respec, you WILL NOT undo the transaction. You will still be down one talent point, and up 10 ability points (or whatever trade you made). The ONLY way to reverse this is to reload an older save.
(With 1 tome of Mortal Techniques)