A review for Square stickers by Brian Balthazor.
The proof looked good. Though the color was not as "true" as I would have hoped. Edges of green on white were not as crips as desired, and for this reason the white font use washed out a bit among the background green.
The sticker quality itself is very nice. So I guess I would prefer your service first allow making one prototype sticker which is sent, then be able to work with someone on your graphics team to get things correct.