most if not all Thai banks list their exchange rate online. If you are transferring in USD (most likely) it will be the Thai bank converting it. I linked Bangkok Bank above. Their rates for USD are good, but 33.
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.61 is still a spread of just under 1%. They usually skew to the buy rate. The current Wise rate of 33.53 is 0.66% better.
This is not a big difference or a terrible rate from Bangkok Bank but if you were transferring $25,000 (for a retirement extension, for example), 0.66% of that is $165. Not saying that's an unfair rate, it's competitive with Wise, but it's a lot more than $25. Thai Thai bank will also charge 500B to receive the money.
If you are transferring in THB, you'd look at the exchange rates for your home bank. This is much less common though and rates are usually much worse, the Thai bank rates are competitive with Wise for larger sums.
you can look up the banks foreign exchange online to try to calculate it. I suspect probably sending USD, most don't seem to have a TT buying rate for VND and the spread on VND notes is large. Good moneychangers like SuperRich or Sakol here in Chiang Mai do have good rates for VND cash so not necessary to change that before coming physically, although need to change at a good money changer not a bank. But transfer the USD rates are likely a lot better than VND. Banks have a spread on USD but it's lower. They also charge a fee 0.25% min 200 max 500B for receipt of international transfers. Wise transfers don't get this fee, you get the full amount.
it's not the interbank exchange rate, it's marked up. The are different buying and selling rates and the spread is where there bank makes their money. That's where Wise saves you money, it is actually the mid market rate and they split out their fees explicitly. If you are sending a larger amount in USD (more than a few thousand) though Thai banks can be competitive. You may also be able to get free wires rather than $25 if you shop around. Much less so on the GBP exchange rate, it's a smaller currency and the Thai banks don't do as good rates on it.
Vietnam issued me a visa without my middle name and then I was denied boarding at the airport. I'd have preferred if they rejected it and I had to do it again.
The problem is compounded by the instructions saying "Your name must be spelled exactly as it appears in the machine-readable zone (MRZ) at the bottom of the biographic data page of your passport."
it doesn't save money, it's much more expensive. But it does give you up to 20 years security of tenure, or even 30 years or life if you find a second hand one. Up to individual if they feel it's worth spending what is a lot more money to get that, but you do can over 5 years, that's the point.
to clarify I'm not having a go at you, like I said my preference is to DIY as well even if it does take a bit longer and I'll only use an agent if the trade off is just too much. I didn't use an agent for my own bank account opening, but it was easier a decade ago.
I sort of figure it has got so much more difficult at this stage, if an agent was offering it for a few thousand baht, that's probably not much more than you'd pay anyway between residence cert and the bank possibly pushing insurance on you. And then you get the bank account guaranteed done without spending a lot of time running around trying to find the right branch and then the right documents (which you probably also have to pay for, I did pay for my residence cert).
There's just a point at which it's difficult enough without and easy enough with that using an agent starts to make sense, that's all I meant. And agents here are not crazy expensive either.