Could you remind me why the 92 effective Mercantile is an important threshold? Which check is it for?
Also, I had a related question about this topic.
I want to leave the quest to the last-minute as well. Does Tanner still need to be with us to persuade the council and do the quest? (i.e. can I leave it until after the main game quest is complete?)
Also, my character has around 60 or 70 mercantile, but nothing invested into Persuasion. I think it is around 12 effective in-game right now. So I could boost that up by what, 20, with 2 heartbreaker armour pieces? I don't know about this "White Dude" chocktail, have to look it up.
Anyway, so this would bring me to around 37 Persuasion, I think. So I only need to invest 13 more at the next level-up and I'll be at 50?
With underpie, it is 95 effective, which means you access last tier at Constantine shop which is probably the best shop in the game for most PC. 92 effective with 7 int is 74 point invested, which is possible from level 13 on, and you can unlock the area where Constantine is by this point: end game gear available at level 13, that's what it means. (Be careful NOT to count on synergy
from persuasion to mercantile to reach 92 as it is capped by level: you can't have points above 75 at level 13 from synergies, above 80 at level 14, and so on and so forth).
You can boost persuasion to 45 with every character having invested 50 points Mercantile and a bit of Tailoring (~64 effective with every bonuses to craft Heartbreaker leather armor and tabis). Proof:
I don't know about Tanner, but you're talking about VERY late game to me. (Unless you want to do Expedition after DC) ?
Edit: failed to read, ignore the remark. Though I still can't answer obviously.
The cocktail is bought on the Drag'n'Drop which is a bar available on all playthrough, accessible with a jet ski:
https://stygiansoftware.com/wiki/index.php?title=Drag_%27n%27_Drop