"Size up your opponent" ability... what skill check?

[Voadam]

The party enters a tavern. It is filled with adventurers and other PC-classed characters of varying levels. Some are lower level than the party, some are higher (much higher).

Short of DM hints ("This one looks way out of your league, better avoid him"), what skill would you use and what DC would you assign for a party member to guess the NPC's level?

In other words, how does the party's fighter know whether to back down from the guy that just poured ale all over him?

Appraise?
Spot?
Gather Info?
Sense Motive?
(Survival? )

I don't give them any rolls. I give them descriptions based on ability scores and equipment and maybe scars and carriage of the person.

I would never say, "he seems to be about 15th level with tons of hit points".

You never know when that orc is an 18th level barbarian or just a jerk joe schmoe warrior until you call their bluff.

 

[bret]

It might help to take the question in reverse. If someone were trying to make themselves appear to be more challenging than they actually were, what skill check would you use.

The NPCs should do Intimidate checks (at a mild penalty if they aren't trying, -5 or so) for the 'aura of fear' that so obviously skilled a person they are.

The PCs should get Sense Motive and Appraise checks.

The Appraise check would be something of the order of: 'Gee, that person has a masterwork sword and masterwork armor -- either they are rich or they know what they are doing. Shoddy clothing -- threadbare and poor quality, so they probably aren't rich.'

When the NPC tries to pick a fight, that is definately an Intimidate check.