I dislike the over reliance of agents and realize that many of their activities are outside the law; however, in the current environment, using an agent to open a bank account is almost mandatory and in no way illegal.
From my understanding, he went to immigration to get a one year extension but since he didn't keep the 800k for two months after the visa, immigration would not extend the visa. Immigration advised him to leave Thailand and re-enter on a tourist visa do he could start over with a 3 month Non O and then a one year extension.
As long as he has the 800k in his bank, he could do this himself, no agent needed.
if you plan to reside in Thailand more than 180 days in 2025, you will be considered a Thai tax resident, which will freeze your UK pension and may make you liable for Thai taxes.