cash on hand is not the same as income. If you were saying you run your own business, cash on hand is business cash how much of that is income how much of that is business expense cash on hand means nothing to the Thai Embassy
if it was simply a matter of more documents, they would have requested them before he was denied. He presented his case to them and they said he does not qualify. That’s the end of the story. Nothing unethical about it. He should’ve done a better job and more research before he submitted his application. 
You’re out the $650. It states that very clearly on the EV application that the application fee is absolutely non-refundable.  you only get one bite at the Apple for the $650 application fee.
Same thing when I tried. They wanted a certified copy of my passport. The certification must be done at the US Embassy either in Bangkok or Chiang Mai trying to get an appointment in Bangkok was weeks away so my wife and I took a train ride up to Chiang Mai and got it done in one week. You have to make an appointment for a notary.  I know you mentioned a certification letter is what they were saying at the bank, but you may want to clarify and make sure is it a letter or a certified passport from the embassy there may have been miscommunication from the people at the bank.