Passage Summary: Most jewelry stores have the person selling the diamond also tell you how good it is, which is a bit suspicious. Gem World says their diamonds have written certifications, so you can trust you're getting a good deal.

Conclusion: Purchasing a diamond from Gem World guarantees you will receive a fair price.

Reasoning: Unlike other stores where the seller assesses the diamond's quality, Gem World provides written certifications for all its diamonds.

Analysis: The argument relies on a significant leap: that a written certification necessarily leads to a fair price. We are told that other stores have a conflict of interest, but we aren't told who performs the certifications at Gem World. If the certifications are done by the store itself, the conflict of interest remains. To strengthen this, look for an answer that establishes the independence or accuracy of these certifications, or one that links the certification directly to market value. A little healthy skepticism about 'written guarantees' goes a long way here.