Mine wasn't denial but was medical. I didn't show any appointments, I just got a letter from my doctor saying I was a patient of hers and the hospital. It was on official hospital letterhead and signed by the doctor.
it all depends on the applicant. My girlfriend had no problem getting a tourist visa for the USA. You just have to make sure you have a reason to return. They also like to see you have traveled before in your passport and have returned to Thailand.
Just did my report in Bangkok. I brought with me a copy of my TM30, passport info page, entry stamp page, my visa and passport. Fill out the TM47 form at immigration and you're good to go.