Not necessarily. sometimes the value is very high due to an item having been rare and traded for high amounts, but it has recently been handed out like candy and is actually borderline worthless - see this hilarious thread about that very experience:
Four Freedoms Firework exploit and other broken items
Other items show a ‘0’ value but are actually VERY valuable, they simply don’t sell on the Market - their sales are via Contract or Hypernet. Research blueprints, and T2 BPCs, are both examples of this.