it is possible to sex a gecko 3" SVL by checking for pre-anal pores. you do not probe crested geckos and you don't really need to be a professional, just need to know what you're looking for. don't let them rip you off.

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sexing

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4.1 snakes, 4.3.2 crested geckos, 0.1 gargoyle gecko, 0.0.2 red-eyed tree frogs, 2.0 devon rex cats, 1.0 betta, 0.1 sun conure, 1.0 lovebird