-Be prepared to be on your feet all day for 6-8 hours. If you're not used to it or don't bring comfortable shoes, you could end up doing some serious damage to your feet.
-Work was outside for most of the day (aside from when you're printing), and on days when it gets into the 90's it can be really uncomfortable. If you're not used to sweating and being hot all day, it's definitely something to consider.
-Not enough hours. Your days may be flexible, but your hours are pretty limited unless you're in management. I was getting about 20 hours a week before I decided to leave, because it just wasn't enough anymore (even though my performance was solid and I was getting good feedback).
-Related to not enough hours, if you're in an area where it rains a lot, be prepared to have your shifts cancelled which will end up giving you even less hours than you already have. Some weeks I only got like 12 hours which is absolutely ridiculous.
-This is probably the worst part about the job, and the part you can do the least about; rude and stupid customers/tourists. Most tourists in general are decent enough, but after 9 months on the job I just became incredibly jaded by all of the rude and entitled tourists that I had to put up with. Some tourists will completely ignore you while you're "line-flowing", or ask you questions about the photos while you're busy (can't you wait until I'm not trying to do a dozen things at once?), or ask to take their photo with their own camera. No, we can't. How do you think we're supposed to make money if we take your photo with your camera? It can also be incredibly frustrating to try and get little kids and babies to look at the camera and have everyone looking at the same time without blinking, and it really depends on whether or not whoever is capturing with you has a good sense of time. If they don't, it can be a really stressful situation.