A fan of StickerMule, but they aren't 'button mule'

I've been buying stickers and labels from sticker mules for a few years now, both for work and personal use. They have been exceptional. But I wanted to try to get buttons to pass out at a convention I'm an exhibitionist for, and the buttons came out less than stellar. The image is darker than my digital copy (and the proof), and some of the text I included in my design, is hard to read in contrast to the background color around it (which was above the 50% brightness threshold, and the text being black). And the overall artwork was not centered on the button by a range of ~1cm on 40 out of 50 buttons. They are free hand-out items for my usage, but I'm not entirely proud to be handing these items out, as they represent me in that exchange. I probably won't be getting buttons made again unless the design is simple and not relying on being centered on the button face.