Bona is a licensed brokerage. An advert still needs its own licence.

Yes. Bona holds REGA brokerage licence (FAL) number 1100313556 and is based in Al Rawdah District, Jeddah. You can verify any Saudi brokerage licence yourself on the Real Estate General Authority's register at rega.gov.sa.

Separately from the brokerage licence, every real-estate advertisement in Saudi Arabia must carry its own advertising licence number tied to the property's deed and to the broker. If you see a listing anywhere without one, that is a reason to ask questions before you go further.

The short version of this answer, with the same wording, is on the questions page.