As with all wild-caught reptiles, the animals found in pet stores have been under stress for some time. As a result, they are most likely suffering from protozoan and bacterial infections, including Salmonella which is easily transmitted to young children. As soon as you can after you take your turtle home, scoop up a fresh fecal sample and take it and your turtle to a reptile veterinarian. Make sure your turtle is given all the medication prescribed by the vet. If you have trouble administering it yourself, take your turtle back to the vet to have it done.
Males have thicker, and generally longer, tails than the females.
Males are larger overall and may be more colorful than females. The time to buy a turtle is not during the fall, winter and early spring when the turtle should be in hibernation. Turtles found in pet stores during this time are likely to be more stressed and suffering from dehydration and starvation than pet trade turtles found during the spring and summer. A gentle tug on a back leg should cause the turtle to strongly pull the leg away. The shell should be firm all over with no slimy or discolored patches.