Sometimes you have to bite the bullet and just be nice to keep everyone happy. But sometimes you just need to throw people out. If you find someone hacking your server for example this is definitely something that should be a lifetime ban. But someone spilling a drink in a keyboard maybe a problem but it shouldn’t be made too big a deal as Keyboards normally dry out and remain working. As well as the fact you probably sold the person the drink in the first place. Keeping children under control could be a major problem though as I have seen in a few internet cafes young children with mothers who are on the webcam. The kids are running around in the store making a lot of noise and irritating customers. Maybe a cheap sweet could be the solution but then again that could just encourage the kids to come every time the parent wants to use the cafe. All in all you have to be diplomatic and fair. Banning a student for example over a trivial act could cost you a lot of revenue if all his/her friends go to another internet cafe with him/her because of the ban. So maybe a punishment duty would be better depending what they have done. E.g throwing fries get them to clean the mess up would get the point across that you wont be walked over but at the same time they don’t get banned. Your probably what the sign is in the picture, basically its a card at an internet cafe explaining no foreigners are allowed because they had a foreigner in the cafe 2 months earlier who didn’t speak Japanese so think the solution is to ban all foreigners. I found it a bit odd as doing something like that in the UK would find me in court as a racist.