Upload & Sell: On
Thanks to all the subsequent commenters!
Cicopo, I don't happen to know how large they'll print it. I wasn't the one who communicated with them. What I do know is that they asked for a file at 600 "DPI", to make a "huge" print. I gave the person who was communicating with them both a straight TIFF from the Photomerge, and also as big a TIFF as Perfect Resize would let me make, which was something over 3 GB. She didn't send them that one, just the native size one.