Design Off Center

My button design was primarily white with a black border around the edge. The artwork on about 1/3 of my buttons was obviously off center, meaning the border was much thicker on one side and thinner on the other. I was planning to sell these at an art event, but I'm not comfortable trying to sell anything that has a production defect. My advice/warning from a designer's perspective is not to have any elements (like a border) in your artwork that would require precise registration to look good. The online proof I approved when I placed my order was perfect, but the actual buttons turned out to be inconsistent. I've ordered buttons before and I don't remember having this kind of problem.