You do not need 400k baht in bank if you use an agent. Everyone who use agent for Non-O does it due to not having the fund in bank. Like others have said, it's bribery, but it's not enforced since the 90s... so.
You need to be legally married with the marriage certificate to get such extension. Yes, it's a practical thing to recall it marriage visa or marriage extension. Let's be real, all the visa names and extensions are overly complicated to understand, it's like me trying to explain the DSM-V to people with no Psychology background. It's a "jargon", so for us, simple humans, I prefer renaming it to something understandable which doesn't denature what it is practically.
Ofc I'm talking about an "extension of stay based on being married to a Thai national". This one-year extension is basically a "marriage visa", which can be extended every year forever.
Troll like Simon should be perma-banned from this group. There are so many threads already and he's polluting with his idiotic non-sense while cracking some "death on arrival" joke which further proves that his post was a troll.