I've seen a wide range of clones. Anything from 2 exposed nodes and sickly to a freaking mini bush with multiple growing tips.

There are a few guidelines to follow:
PESTS: A guarantee that the clone is pest and disease free merits higher cost
ROOT STATUS: A clone with visible roots is worht more than one that is only partially rooted.
STRAIN: An elite or medically valuable strain, or one that is notoriously difficult to propagate, is worht more.
HEALTH: Don't pay more than $10 for a clone that you have any questions on its health, or request that you be given extras to guarantee that the number you PAID for actually SURVIVE.
SIZE: More nodes and more growing tips makes for a more valuable clone