@Larry ************
income doesn't have to be into a Thai bank IF your home embassy will give you a letter certifying your income. Some countries still do this and people from those countries can still do it that way. The US stopped these (as did most Anglophone countries other than Ireland) so Americans can't use that method. Some Europeans can still use this method.
It comes down to whether the embassy will actually verify your income. Historically the US and many other embassies just certified a personal affidavit, they were just saying "this person said this in front of me", they didn't actually check that the income was real. So many people got letters without having to prove income. Thai immigration started asking embassies to actually verify and stand over these letters. Many embassies were unwilling or unable to do this, so stopped issuing the letters entirely.