I am new the neighborhood here. When setting up shop it led me to examples of gigs, and I poked around myself. I have seen gigs with more examples then I was able to load, by way of the site. In order to have more than three examples in your gallery you have to obtain a certain level, or how does that work, getting more examples in your gallery?
I am a top rated seller and I cannot attached more than 3 files to the gallery section.
The samples you see in some other gigs are probably a preview of a delivered work (completed orders)