I've had more than one instance where a distant framer upsold a gallery wrap print customer to a full framing treatment, and then framed the piece INCLUDING the visible mirror image surround intended for gallery wrapping. In one case an irate customer asked for her money back plus the cost of the her framing job, due to my "bizarre and capricious" printing error. I guess people don't really look at the print until it's on the wall, and I'm pretty sure many people including certain framers don't know what "gallery wrap" actually means, however much they may nod their heads and grunt affirmatively when I describe it.
To this end, I always include a statement on the print itself just outside the mirror image + 3 inches of white. It says "This image includes a 2 inch wide mirror image around the entire central image. The mirror image is intended to wrap around the sides of gallery wrap stretcher bars. In the event this image is to be presented with a frame and possibly a matte, the portion of the image displayed should not include the 2" wide mirror image border."
It is not sufficient to merely include those instructions on a separate, enclosed piece of paper. The message needs to live right there on the print in biggish type.