This may be unpopular, but it needs to be out here.
Tipping is only a thing in the USA where waiters, and waitresses, are not paid a living wage for some reason.
That should change. It isn't normal, or customary.
What is the idea of after being paid for a service, to stick your hand out, and ask for more for the service you just charged for?
I know it is Fiverr, and not the artists.
I don't know which country Fiverr is based out of, but this tip thing should be taken off.