During the fight between Anya and Clarke in front of the drop ship they are both covered in grime, and after Anya hits Clarke with the log Clarke's face becomes increasingly smeared with blood. Throughout the scene, you can see Clarke's face switch between grimy and bloodied at least a couple times, most noticeably in the shot just after Anya tackles her into the ground and the following one.
When Jaha frees himself from the missile, he's taking out bolts that could have only been inserted from the outside, and there was no one else on-board to perform this task.
When Murphy, Finn, and Monroe were starting to lower Bellamy down the cliff to save Mel, a male voice could be heard saying, "All right, ease it out slowly." None of the characters on-screen could be seen saying these lines, and the only other character present was a woman, Mel, who was waiting to be saved.
Grounders have shown pin point accuracy when they ambush, killing or severely wounding a character with single attacks. However when Bellamy's group is trying to save the girl from the cliff, the grounders "conveniently" miss most of their range attacks.