The model works. Sole Supremacy moves units, a lot of them and they are primarily cashout. I'm almost certain they rarely do consignment unless you're local. I personally sold them about 120 pairs out of my personal collection late last year and got about 10% less than if I would have had my shoes sitting at a consignment shop for 6 months.
For the seller it really is a no-brainer. The one thing you're overlooking is that the most successful stores now are the ones that are well financed. The days of opening a consignment shop and expecting every person in your local city to bring you pairs is almost dead and gone considering how many stores folded in the last couple years.
Some with customers shoes. Just disappeared.