I opened mine 10 years ago more difficult now you should be ok with non o or oa visa ,proof of address,and probably a Thai national who will vouch for you
OR ANY NON TOURIST VISA
I opened my account with kasikorn but think it's pot luck who you talk to
Don't know what country you are from but I think your better to bring your own currency,maybe a small amount of baht for couple of days,DO NOT CHANGE THE MONEY IN THE AIRPORT (super Rich ) ok but think still shut,use one of the independent exchange booths for the best rates when you out and about
I opened one on a tourist visa for me it was because I was coming three times a year,I have family here,and KNEW I would need one in the future,but even 10 years ago it wasn't easy went in a few bank and my wife had to sign as guarentor
trouble is it's all about face in Thailand,I think if they don't know and they ask a superior. They are admitting they don't know and to a Thai they will lose face,assume that's why you ask again someone else knows and hey presto you get your bank account
Used to be able to walk in any bank with your passport,but now not easy,do you have a Thai wife or friend who can sign as guarentor which is what I did with kasikorn
One indivdual who is also insurance agent and a travel company both based in thailand seem very genuine both have good reputation,but as you say plenty of sharks preying on people