I wouldn't say it means a fixed amount. As long as you have an amount of money in your Thai bank account and monthly transfer that always comes to at least, or more than 800k THB.
I flew OmanAir from Manchester back in 2018. Very pleasant flight. Cabin crew very polite and professional, unfortunately for whatever reason they no longer fly from Manchester I believe.
There's loads of experts on here who seem to resent if someone wants to have a representative to handle all their immune gration affairs etc., If he wants to pay a rep., to handle it all that's up to him. He's asking for advice not criticism.
You think it's bullshit? Well any monies you have and transfer to your Thai bank account, if your in Thailand more than 179 days, it is liable for tax. Thailand has brought in this rule in line with Western countries.
Airlines don't have open tickets these days. When I was living in Thailand in 2000 to about 2006, you could buy twelve month open tickets with all the airlines I used.
No such thing as required by law. I flew in & out of Thailand dozens & dozens of times on one-way tickets. It's Upto the airline whether they require to see a return ticket, or a ticket onward out of Thailand. I was never ever asked at Thai immigration for a return ticket, only presented my passport and the immigration card, can't remember which TM it was that you were given in-flight.