The official requirement any organisation should have to be allowed to issue DTV is :
„Tourism Authority of Thailand Certification“
What you can do is ask your embassy of Thailand in your home country or anywhere else and write an email if this certain school is officially qualified or not, should have (TAT) or (MHESI) certificate.
Reddit or google or Tripadvisor is all heresay without evidence. To be 100% sure ask the embassy
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