In order to get full payment in advance, you need a client who is willing to give full payment in advance. This in turn means either
--be in a line of business where advance-in-full is the industry standard (off the top of my head, keeping in mind that I'm in the US and this is about services, not products: rentals, travel, education).
--have a very trusting, gullible or stupid (adjective depends on your own position in the arrangement) client.
--or, OK, #3, have a de facto monopoly
Turn it around, please. Under what circumstances are you yourself prepared to pay in advance for services that have not been received?