Not every beachfront resort actually controls a private stretch of sand — in Thailand, all beaches are legally public, but some resorts occupy long enough, secluded enough frontage that it functions as effectively private.
What "private beach" really means here
Legally, the beach itself remains open to the public. In practice, resorts on isolated coves or with restricted road access (much of Cape Panwa, parts of Bang Tao and Natai further north) see very little foot traffic beyond guests.
Where this is most true
Naturally secluded coves with limited public access points — as opposed to long, open beaches like Karon or Patong, where "beachfront" absolutely does not mean private in any practical sense.
What to check before booking
Ask directly whether the resort's frontage is a shared public beach or a genuinely secluded cove — marketing language alone often isn't a reliable guide.