The starting point is of course, is checking all the normal credentials like CSLB, insurance and references. But perhaps most important is deciphering whither he is a good Skylights craftsman or not. If the painter is only following the industry standards, he is falling way short of good craftsmanship.
Red flags with Irvine Skylight advertising are as follows:
1) Advertising for a trade that they are not properly licensed for. See "The right contractor’s license".
2) False reviews.
3) False or exaggerated claims, i.e. years in business.
4) Using terms like: "combined years of experience". The aggregate years of experience, of multiple individuals is irrelevant.
5) The most important credential is not how many years they've been roofing or installing skylights, but the quality of craftsmanship or techniques used during the years of experience. If a skylight installations contractor employ’s poor techniques or a lack of understanding of his craft, the quantity of years are irrelevant.