My only concern is if the agent gets your extension from Bangkok and not from the province where you live. If they get it from your ‘home’ Immigration Office then that’s fine, if not it would just niggle at me a little.
you can’t use the income method for the first year because you won’t have 12 month history of transfer from overseas each month. After that it’s one method or the other.
You can’t use it for the first year only subsequent years. You’ll need to be able to transfer 800k into your Thai bank account immediately when you open it for the first year, or pay extra to the agent if you use one - but that ‘might’ complicate it for the second year.
it needs to be transferred from overseas each month (and clearly identifiable as from overseas) and it must be at least 65k every single month without fail.
I’ve heard of some offices also insisting on proof it’s from a pension, but I think it’s a minority.
All of them have the requirement, as it’s the actual rule from Thai Immigration , but it’s a matter of how the check in staff decide to deal with it. I’m on a Thailand forum and many members have been asked at check in. Some have had to buy an onward ticket on their phones at the airport to be allowed to fly. Other check in staff don’t bother so it’s inconsistent.