Uhm there's nothing arbitrary about level... I determined this by deciding what level in the sandbox I want him to inhabit and thus be an appropriate challenge for.
This is why I said semi-arbitrary.
I assign his class based on what his profession is... so again not arbitrary.
Expert or commoner? Semi-arbitrary at best.
Uhm, actually I'd randomly roll his stats so yeah I guess arbitrary but then letting fate decide means no bias on my part which I enjoy in a sandbox. Skill points and feats are based on the concept for the NPC... so again... not exactly arbitrary.
The number of them you get and how you spend the non-core ones
absolutely is arbitrary.
Uhm... your entire method was as arbitrary or moreso than the one above
Nonsense. I didn't make the petty distinctions about the exact physical stats. The level you claim to be non-arbitrary. The ability to bake well is non-arbitrary.
and still leaves entire areas of the NPC blank. Your method leaves me with no information to guide me if the players decide to, instead of challenging him in cooking, do something else such as arm-wrestle him or lie to him(as players often do).
Nonsense. Giving the level gives me three values. Easy, medium, or hard. I should be able to work
that one out based on any text I have. That is
all I need. If you are really telling me that your description of a baker doesn't say whether he'd be easy, medium, or hard to arm wrestle then I wonder whether you think fluff should match rules at all.
And as for 'lie to him', lie about
what? Because it's going to be a lot harder to lie to him about the quality of flowers than about gems. Bluff isn't just lying.
In my method I have everything I need to determine what happens regardless of how the PC's choose to interact with the cook.
So do I in mine. But I spent about three seconds thinking about stats ("5th level. Good at baking. Lousy at noticing anything outside the kitchen") You on the other hand (assuming he's a commoner) have had to roll six ability scores, allocate twenty four skill points (for an average 5th level human), deal with 5d4 hit points whichever way, calculate AC and saving throws, and anything else I've forgotten. How long does that take you to do? Two minutes per NPC? Five?
And there's no significant difference between our NPCs that isn't within one standard deviation of a d20 roll - within one standard deviation and for a one-shot NPC, who cares? I don't think anyone's worried whether his profession (baker) skill is +11 or +13 as long as it's not +2 or +27.
And because I have a decent narrative system for the NPCs the stats are
obvious. Describe them and give one number (the level) and everything else just falls into place. For his combat stats, he's massively outclassed so he's a minion. Describe him physically and I have whether to use Brute or Skirmisher Minion stats to see whether he can escape (unlikely either way).
This means that I not only have adequate numbers for all his skills, I can create them
at the tabletop without the players having time to notice. And I still have clear numbers to use.