Stickers for Cartooning Class

I had a little illustration I use for spot art for my comic strip. I threw it in it's own .png file and sent it off to get printed because I wanted to be able to give a few away to a cartooning class. I've ordered with Sticker Mule before, but every time I send in something I'm worried I'm doing something wrong because it really is that simple. I just made sure the image was at a good, clear dpi and sent it off - They crop it. They adjust it to fit the size. etc. The quality is great, both in regards to the vinyl the stickers are printed on and the final result of the image. Whatever color you send them, in my experience, is what you're going to get in the finished product. And I've never received anything pixelated - the image is always crisp. Is Sticker Mule a little pricier than what you'll find from other bulk printers? Yes, but their quality is slightly above that of other vendors and really the convenience more than justifies the price. I dunno what magic elves they have working for them but Sticker Mule, you better be paying them well. Your people do awesome work.