Hobbyists typically (but not always) care about low prices. Professionals care much more about quality. We’ve added a feature for those professionals: the ability to search PCB manufacturers based on their quality certifications. You can narrow your search to those companies with ISO 9001 certification, IPC 600 certification, either certification, or both certifications. Just choose one of the options in the “Quality Certifications” field.
Of course, if you don’t require your PCB supplier to have certifications, you can specify that quality certifications are “Not Required”, and PCBShopper will do its search of all companies, just as it has up to now.