Gotta work on a bit of lore before I make the hook.

Once upon a time, auctions were stage shows, deliberately designed to maximize the slaves' powerlessness. Auctioneers would bring up one or two slaves at a time, crow about their features, and sell them off to the highest bidder. The trouble was, that could take a while if there were more than a hundred or so. Conquered cities yielded thousands of slaves. So instead of auctioning each individual slave, the traders assigned fixed monetary values to various slave profiles and sold them in displays.

* Language Fluency: +2 gold for understanding, +3 gold for ability to speak it, +4 gold for fluency
* Youth: +1 for childhood, +2 gold for adolescence, +3 for an adult, and +1 gold for every 100 years estimated remaining lifespan. Goes to zero if past prime/elderly.
* Strength: +1 gold for average build, +3 gold for a fit build, +5 gold for a bodybuilder/soldier
* Attractiveness: +1 gold for average/decent looks, +2 gold for catching eyes, +5 gold for a stunning model
* Professional Ability: +1 gold for competency, +2 gold for expertise, +3 gold for genius

Frandur, for example, would earn +4 gold for his fluency in Common, +3 gold for maturity, +2 gold for having about 200 years left on his lifespan, +5 gold for being a bodybuilder, +2 gold for his eye-catching looks (most notably his gorgeous hair), and +10 gold for his competency or expertise in multiple professions. He would be worth a whopping 25 gold, a stunning profit - if the slave traders knew all his abilities, that is. Captured people aren't particularly eager to earn their captors a profit, so much of the challenge is getting slaves to reveal their abilities.

Yanduin would fetch +3 gold for his rough understanding and speech of Common, +3 gold for maturity, +8 gold for elvish youth, +5 gold for being a bodybuilder, +2 for his eye-catching looks, and +1 gold for competency in basic architecture. 3+3+8+5+2+1= 22 gold.

Lanik, if he were sold at auction, would fetch +4 for fluency in Common, +3 gold for maturity, +5 gold for being a bodybuilder, +1 for average looks (i.e. not being ugly), and +1 or +2 gold for his mechanical inclinations. 4+3+5+1+2= 15 gold.

Erudessa would fetch +4 for fluency in Common, +3 for maturity, +3 for fitness, +5 for stunning beauty, and +2 for mechanical expertise. Given her youth, most evaluations would put her remaining lifespan at about eight centuries, but they have no idea yet that she is immortal. The auction house would value her at 20 gold, if her rare silver hair didn't warrant putting her on special auction.

For comparison, a typical foreign human slave fetches +0 gold for not knowing Common, +1 gold for average looks, +3 gold for maturity, +1 gold for average build, and +0 gold for having no other marketable skills (besides farming or housekeeping), total value 5 gold. City dwellers often fetch little more than 4 gold (usually +3 for adults, +1 for either average looks or average build, but not both). Children are even worse off, earning no more than 1 or 2 gold, and the most profitable slavers either leave them, raise them, or sacrifice them, since feeding and sheltering them can cost more than they earn.