For the yearly extension there is no proof of funds origin but for the 90 day in country Non-O visa at MOST offices you show that it came from abroad into a thai bank account in your name only
CHECK with your immigration office to see what they require.
So far the O/P is applying in Mae Sai (Chiang Rai) yet my experience is in Bangkok,
@Tracey ***************
posted about Hua Hin and
@Ross *******
posted about Surin.
NONE of our experiences are with the office the O/P will use 🙁