Cosmetic Injuries are typically easy to overcome as the fish will heal. What do you mean by hurt bad? If you can nurse the fish back which I always do for sick fish i see in lfs I don't see any harm in buying it. The part that pisses me off the most is when lfs don't even take the time to make their fish healthy after shipments and I see them dying. If they were going to do that, just give me the fish for free lol. Eating healthy is good and yes they are pigs..make sure to keep your tanks clean, they are a bit messy.
Anyways...going off the wall here, Your flowerhorn is a zz Red Dragon. It may look like a female right now, but I actually think its a male. What size is it? I've had males display no head bump, and then out of nowhere bam. Venting is probably a more accurate way to sex your fish when it grows out.