For Bangkok Bank its Certified copy of passport i have the document beside me now me now which i used 1 year ago to open my Thai bank account on a tourist visa. This was from the British Embassy in Bangkok. There is nothing on my document about my thai address.
On the letter it says
I do hereby certify that this is a true copy made by me of an original British passport presented to me by (Name), Identified as British passport number ()
The process was quick and simple in and out in 10 minutes at the British Embassy i believe the cost for them to verify the document was around 25 pounds.
Once i handed the certified copy of my passport document from the British Embassy to the Bank thats all they needed and i had my Bank account opened in 15 minutes.
Bangkok Bank are the only interested in tourists from my experience the rest you are wasting your time attempting so best to stick to Bangkok Bank.
The process really isnt that difficult if you make an appointment and get that document from your embassy. The only cost is the embassy appointment but certainly a lot cheaper than paying an agent.
I guess the only reason i can see to use an agent is if you are not going to be in Bangkok to be able to go to the embassy.