Which cavy fault deals with presentation and enhancement in a show?

Unkempt fur is indeed a crucial fault in the presentation and enhancement of a cavy during a show. A well-groomed cavy with clean, well-maintained fur not only looks more appealing but also reflects the care the owner has taken to prepare their animal for competition. Judges typically assess the overall appearance of each cavy, and unkempt fur can detract from its visual appeal and overall presentation. Proper grooming enhances the physical characteristics of the cavy, allowing its desirable traits to shine through during competition, which can significantly affect the judge's impression and scoring.

In contrast, the other options do not specifically address the aspect of presentation and enhancement. While correct body size, strong color patterns, and absent markings may play roles in the judging criteria, they focus more on structural and aesthetic characteristics rather than the grooming aspect that directly impacts how a cavy is presented to judges.