The happy ending places are usually pretty easy to spot from reviews or their website if they have one. A few indicators:

• The images they post online are just attractive women possibly giving massages. The focus is on the person giving the massage, instead of general relaxing imagery.
• Reviews are split down the middle between 5 stars with no details and 1 stars complaining about short, half-assed massages and requests for tips before the massage ends
• The building itself has all the windows covered and very little advertising except for a sign to reassure clients they have the right door.