as I said the source of the income for a marriage extension depends on the particular office. I know this because I am on a marriage extension myself and my office does not allow income from outside Thailand. I very much doubt it is the only one as have read it many times on this forum.
You are absolutely correct that going from using an agent is hard but it isn't impossible. The first two things you need to look at are:
1. Because you have a 1 year extension based on 800k Baht in a Thai bank. When you apply for your next extension you must show 800k in a Thai bank on the day you applied (2024) and that 800k Baht was maintained for the next 3 months. Then for the remainder of the year the balance did not drop below 400k.
2. Will your immigration office allow you to extend for the reason of being married to a Thai national based on income. Some (most) offices require the money to be generated in Thailand therefore you will probably need a work permit. Some offices also require you to be married for a minimum amount of time.
If you can satisfy the above then ask for a list of requirements. It is a much longer list than the retirement but once you have done it once you can just repeat in future years.
that is my experience too. But I didn’t use an agent to grease the wheels all my accounts are 100% legitimate. I have multiple bank accounts with 4 different banks. If one of the banks decided to change the way they do business I would just move my money around.
funnily enough I also had an issue with Qatar at Manchester. I have a Non Immigrant O and the guy at check in was not going to allow me to fly without an onward flight from Thailand. I explained what a non immigrant O visa was but it was pointless. I asked to see the supervisor and luckily she know what she was looking at so problem was resolved.
with a one way flight you need to check with your airline if they will alow you to fly. A couple of the airlines need you to show proof that you are going to leave Thailand in the 60 days.
Check first and then you won't have any issues on the day you fly.