I ordered an adult male European Pond Turtle that was confirmed via email to be available. I received an adult female today and took a photo of the cloaca / tail that is proximal to the plastron. Males have a distinctively larger, muscular tail with the cloaca closer to the distal third of the tail to facilitate mating. Despite the picture, they insisted it was a male and that their "guy with 22 years experience" says it is. "We appreciate your understanding the complexity that often goes with identifying the sex of many animals." Perhaps he thought the turtle identified as male. They also cited their proviso that "sexing" of turtles is not guaranteed. Well they advertised this as an adult male for sale. This "male" turtle is also gravid with eggs that can be palpated.
Update: The turtle in question was found dead in my pond 3 days after delivery. Cause is unknown. I dissected the turtle and found eggs and ovaries confirming the gender of the turtle.