I would imagine that part of a reputable breeder's "reputation" is their ability to ship effectively, so, by definition, reputable breeders are likely to be credible shippers. To be more sure, you could always ask a breeder you're considering either how they package and ship their reptiles, or whether they use the shipyourreptiles.com standards (you can go to that website and learn about it as well so you know what it's about).
Aliza