It's essentially a bait-and-switch tactic. Clearly, the pictures provided won't accurately represent the SW available, but I can assure you that many of these Asian ads do indeed have some SWs available. It's not a scam per se; rather, it's more about not receiving the exact person depicted in the images. However, the services offered are genuine.
I once encountered an Asian sex worker who was a hidden gem. Unfortunately, I couldn't locate her again. Her ad was gone before I could even write a review, and she changed her number as well. It's a hit or miss situation, but generally speaking, you're unlikely to be scammed unless the advertisement is overly vague.