don't take the soft power activity serious, they only need a ticket for 5 years entrance in Thailand and abuse the DTV for this, discussion with them is useless.
That is incorrect, it is designed to be the correct option, that some immigration offices seem to have problems with it or don't like is a different story.
What kind of documents you showed for proving the financial requirements.
It should clearly showe there is 500K last month and your name and address.
In the story I don't see the working full time discussed by immigration, only the financial documents, so it would be helpful to know what they did think was wrong about it.
That they cannot guarantee an extension before checking is normal, otherwise checks would be of no use.
Of course you might be lucky and in Thailand it is possible to buy everything, but that does not make it legal, and one of the group rules in this group is we should not promote illegal ways to get visa.
I understand your opinion is not from own experience but from what you heard, my experience when asking for information does not need these stories, Immigration office of Songkhla was very friendly, if the stories were true they easily could have not answered at all or just advice to do a border bounce.
Since a lot of people here think that visa requirements stop as soon as they got approved, I can understand all those people complain about extensions in country.