People who question certifications from Thailand are probably doing it due to ignorance and due to the reputation of the few insanely large ops on the island. There is a lot of great shops and great instruction on the island. Unfortunately a few of the giant dive factories where you are basically just a number have given the island a bad name. A lot of people do the zero to hero thing at these shops and end up having professional certifications with not a lot of diving experience. I have done courses in Southern AUS, northern AUS, Hawaii, Massachusetts, South Pacific, as well as Koh Tao, and I can attest that there are some very good shops and instruction on Koh Tao. I was at New Way while I was living on the island, although everyone who was there when I was there is now at different shops. Dave, who was one of the head instructors at New Way, left and opened up Roctopus Dive which has been successful and grown a lot and is a great shop if you are looking in Sairee. I'm sure New Way is still a great shop as well. Master Divers has always had a great reputation as well if you are looking for a shop in Mea Haad.