I just wanted to share my positive experience at the Royal Thai Embassy in Colombo, Sri Lanka applying for a SE Non-O Visa, family purpose.
First thing to do is to book an appointment online (they usually have availability every day of the week Mon-Fri) specifying the type of visa you're applying for and print out the confirmation email. They don't let you enter the embassy if you don't have the appointment paper with you.
I would say that for me the only struggle was finding a printing/photocopy shop in Colombo.
I had all the documents they required, except for my wife's Tabien Baan original house registration (we only had a copy), her original passport (which we forgot at the hotel) and the original bank statement of mine with bank certification (I could only print out a statement from my online banking and auto-certify it). The officers were not fuzzy about us not having the originals, they just took the photocopies.
Account balance required is 110.000 SL rupies, which is around 20.000 THB.
Officers are Sri Lankan and they do all the process, but after you hand them all the documents they have a Thai officer review your application and see if there's anything missing or it's good to go.
SE Non-O visa cost is 13.000 SL rupies, approx 2300 THB, passport pick up is after 5 working days. While your passport is with them, I would suggest always carrying a photocopy of it + the visa application receipt and it's all good.