We were a pretty early adopter of the Garnet Marketplace app. It has enabled us to expand the brands that we list and automate a lot of the work that was done manually prior to installing this app. Francois and his team were able to customize some things (extra cost) to improve the workflow for our needs.
Pricing is definitely not cheap (hence the 4 stars instead of 5) and has increased since we installed it, but there are a lot more features that are included in that higher price. I think Garnet should offer more tiers and have them based on the number of products, vendors and orders. Just my 2¢