These guys are right to a point, you need to prep and use paint that can withstand unusual temperature changes and flexing. You also need clear coat to protect, the kind they use for cars works well, take you skis down to an auto body shop and ask them to use their leftover after doing a car to give your skis a few coats in exchange for a 12 pack or something.
The problem is, even if you do everything right, the paint will still chip off. Normal ski graphics go under layers of plastic, so scratches resulting from your skis banging together that would normally not damage a graphic will ruin painted graphics, even with all the clear coat in the world. The upside is of course, since you did it yourself, when it chips and cracks too much you can always paint something new.