Crazy money. If an agent gives advice and quality assured your application before submission I think a 10-12k THB is fair. I woukd also expect they off a full refund if rejected as long as you were fully honest with them
Do it yourself. Ask any questions here. If you really want an agent choose one that offers money back guarantee and then only for document checking before submission. Good luck
I reckon you are less than 1% - in fact even less on a DTV. In 30 years of business trips globally, for household name companies, I was asked at a border for a business card twice. Once in the UK as a British citizen (I could not look more British) and once in Japan :-).
They are strict with everyone. The actual immigration office in Chiang Mai are also very easy to deal with and helpful too. Only recently threads in Expat Groups praisng them. I have never seen that for any other offices.