I do not know much about wise, you can send money to yourself but where is it now? I think the only way to pay is via a bank draft, issued with money in Thailand. If u want to take it out again you need to prove where it came from, in my BBK bank account all inward remittance is labeled "Foreign Telegraphic transfer" and as such that money can be repatriated! How you do this with wise, i do not know.
you cannot get a banker's draft unless the money was transferred to your account preferable from outside Thailand! Since you have no adviser, I suggest you find one! If there is a time limit in your agreement, you lose your deposit!
Did you buy this condo through a realtor? If so they should be helping you with this! If not, maybe you should hire a lawyer to help you! It's not uncommon for the seller to have a power of attorney at the close! What happens at close is you pay the closing costs in cash to the cashier, you get a receipt, you take this to the registrar, the seller presents the title doc, your name is put on the title doc for all to see, you hand over the draft and you get the title there and then. Within a few days you will get the blue book, if u do not speak Thai, this is gonna be a challenge! On the day of closure if you fail to close you lose your deposit, so do not f*** it up!
I believe the statement saying "that those people from countries which have a double tax agreement with Thailand will pay no tax in Thailand" to be incorrect. In my opinion, double tax means that you will receive tax credit for taxes paid outside of Thailand. So, if you are assed as having to pay usd200 in USA and usd300 in Thailand, In Thailand you would pay 300-200=100 dollars in Thailand.
Usual process is you pay a small deposit, you make an appointment for close at the registry, you have in cash the money for taxes and a banker's draft made payable to the seller, you exchange Infront of the registrar! anything else is dangerous or illegal!