I'm a vendor as well as a customer, so here's my thoughts :)

1. Quality products. Not stuff that's been thrown together in a day and upped to the store for $5. Those sorts of items should go into free stuff.
2. Victoria 4 characters that just look like Victoria 4 with some makeup.
3. Daz, Poser Pros and then here.
4. Uniqueness and quality.
5. Low quality, pokethru (it's unnecessary) and not working as described in product info.