The stress of travel might have made them worse, but they were definitely sick when they arrived. One was half yellow and floating around on the current, and another (in the photo) was quarter yellow. It's partly my fault for not paying enough attention to them in the Bird Barn's tank and not paying enough attention to the employee, but I assumed he'd be a better judge of fish health than me. I'd seen one near-dead fish in their tank but didn't worry much since it seems pretty common, but I think that was one of the ones they gave me.
By this morning three were dead, and couple more looked like they had very fine, feathery, fungus-like growth. I took them all back to the shop and got store credit, and they said if my own fish showed any signs of sickness in the next couple of days to let them know and they'd deal with it, so I guess that's the best I can hope for.