Thailand lets foreigners own a condominium unit outright, in their own name, which is unusual in the region — foreigners generally cannot own land here. The catch is the '49% rule': the total floor area owned by foreigners in any single condo building can't exceed 49% of the whole building. The other 51% has to stay in Thai ownership.
That quota is checked at the Land Office when you register the title, not just when you sign a sales contract. If a building is already at its foreign-ownership limit, you cannot register the unit in your name even if you've already paid for it — which makes checking the building's current foreign-quota percentage before you sign anything, not after, one of the most important steps in the whole process.
The purchase money also has rules attached. Funds have to be transferred in from abroad in foreign currency, and the receiving Thai bank issues a Foreign Exchange Transaction (FET) form confirming that transfer. You need that document to register the title at the Land Office — money already sitting in a Thai baht account generally won't satisfy this requirement.
Renting the unit out afterward is usually fine if it's long-term — most Bangkok and Phuket buildings allow leases of 30 days or more without extra licensing. Short-term rentals under 30 days are a different story: that can cross into hotel-business territory, which requires a license, and managing it yourself would require a Thai work permit.
There's been ongoing talk about raising the 49% quota or allowing new leasehold structures for foreign buyers, but as of the most recent reporting, none of those reform proposals had actually been enacted — the 49% rule remains current law. Given how much money and legal exposure is involved, this is a case where a local property lawyer's sign-off is worth the fee.