Image quality is good, but image printed dark.

What looks fine on any screen I view the art on, has printed darker on the product. My background color has what is supposed to be about a 75% grey color (it is #424242). What I have on my magnet is so much closer to the black line work that a lot of the design is lost. I'm glad this happened on an inexpensive special offer rather than on an order where I payed full price, but the printer should calibrate to better match what the artists intend. Either that or warn artists that prints will end up darker so we can adjust files. Other than that, the print quality seems good. The issue seems to be the printer isn't correctly color calibrated, or the images aren't run through a pre flight to optimize the images for the output device.