If it's a new, boxed device, I don't think they'll know unless the SW-VER code on the box tells them: It's not evident from the code to me. I can tell you that the new one I got from ATT in August -presumably one of their last ones- was a 1.3. Is it returnable in case you don't get what you want? Good luck with your new Focus.
If you want a decent condition used Focus v 1.3 check out Cowboom.com. Their prices on phones are really competitive and I managed to get the Focus for $90 shipped winning an auction.
They shipped it within a week. The bottom housing under the screen on the bezel had some scuffs but the screen was really nice and it came in working condition. I did a hard factory reset, updated it to Mango and have been really pleased ever since.