A skylight only leaks when it is flashed badly. We curb mount every unit, fit the manufacturer flashing kit and seal the seam rather than taping over it. Glass on an existing curb can usually be swapped without opening the roof at all, which keeps the job to a single morning. New openings are cut, framed and finished by the same crew that does the roof, so nobody points at anybody else later. The price per skylight is fixed in writing.