Hi,

I was told by the Seller company that a work permit is necessary along a copy of passport and a foreign transaction form (already in my possess) to register a condo unit under my name.

Is that true?
Is it a work permit really necessary for it?

Work permit, letter of residence from immigration or copy of your yellow book (Tabien Baan for Farang) if you have one should be sufficient. Ridiculous to say you need a work permit. Hundreds of retirees own condos.

Thanks, how to get a letter of residence from immigration and how much is it?

What you need is the Foreign Exchange Form, your passport, the letter from the Development Juristic Condo Manager stating that the Maintenance fees are paid and no outstanding payments existing, the list of all foreign held units in percentage with name of all foreigners in Thai on it. If you sign a Power of Attorney abroad, this PoA should be notarized, otherwise if signed in Thailand showing your visa entry stamp showing that you resided in Thailand during such time. In lieu of the Foreign Exchange form you can also show other evidence where such funds come from, for example is you sold one Condominium and you use the funds to buy another unit, you can show the evidence of transaction to use for registration.

NO Work Permit or letter of residence are not necessary, never heart that in 15 years working in this field.