Well, I picked all seed diet because it is a widespread issue... I can't tell you how many regular customers I tried to convince to feed their birds more than just seed mixes and the new owners more often than not assumed you just buy a bag of seed mix like you'd buy a bag of dog food and that's all there is to it. If I had to guess, I'd say the majority of pet birds are being fed strictly seed diets and it's horrible for them.
Selling/ Buying unweaned babies to/by inexperienced hand feeders is an equal issue for me but I couldn't pick two.