Yields by city, what the building rules allow, and the daily-rental problem.
Gross yields in Thailand generally run higher outside Bangkok. Pattaya is typically quoted at 5–8% gross, Bangkok at 4–6%. Gross means before common area fees, sinking fund, management commission, income tax, vacancy and furniture replacement — which together commonly take a third off.
A developer's guaranteed rental return, usually offered at 5–7% for the first two or three years, is a marketing cost priced into the purchase price. Treat it as a discount spread over three years rather than as a yield, and ask what happens in year four.
Renting a condominium unit for under 30 days is, in general, operating a hotel under the Hotel Act, and requires a hotel licence that a residential condominium building will not have. This applies regardless of what the platform listing says or what the seller told you.
Enforcement is uneven but real, and the practical enforcer is often the building's own juristic person, which can and does bar short-stay guests from the lifts. If your investment case depends on nightly rates, verify the building's rules and the legal position first — not after.
Letting on leases of 30 days or more is ordinary residential letting and is not affected by this.
Rental income arising in Thailand is taxable in Thailand, whether or not you are resident and whether or not the money is paid to an overseas account. There is a standard deduction available against residential rental income, and a personal income tax return to file.
If you are tax-resident elsewhere, check the double tax treaty position rather than assuming one country cancels the other.