The problem is even if you ban them its not a loss. Shards make millions very easy and can be done from level one, I've seen people on FFXIVCore receive like 4 Buddy Keys, and he just multi-bots on all of them, making 4m a day, (at 100k a stack), and if they get banned, he just asks for more buddy keys and so on lol.
There is not much SE can do right now sadly. Also the ONLY way you know if its a bot or not is to see if they craft for like 40-50 hrs straight non stop even tho humanly possible i doubt would happen, you'd fuck up or sleep would get you. Just spending 5-10 hrs infront of the npc hasty handing fishes is not enough evidence to proof this is a bot.
also the GM reply wouldnt work, you'd just make the bot reply based on reg-expressions and then put in count detections to ensure you dont keep replying with same thing. It is also quite unprofessional and a GM wouldnt do that. Best bet for GM is to just log it or im sure if SE really wanted to they could make a system that detects long-extensive crafting hours and flags a GM.
