Hanoi is to be avoided, they cancel for no reason, I've seen the exact same application cancelled in hanoi then the same docs given in hcmc and it was approved
For the monthly option you need to show in your THAI bank account, monthly money transfers from overseas, you must also have a minimum of 12 months of this happening
I know personally many people denied because they didn't have the funds in for 3 months, also know people who had money in there just a few days and was approved, all at the same embassy
some people are just walking red flags, they look suss, or have a suss history, It's not like everyone is being shaken down. I flew home to australia once and was interrogated for 3 hours because I didn't have any bags, I think some people don't want to admit it but they look like they couldn't possibly have 500k in the bank