When Justin dunks his head in the potion and comes back up, you seem him run his fingers through his hair and make it stick up. Then the camera goes to his parents and then back to him where his hair is down all the way again.
In the end of this episode, Beware Wolf, when Justin is sitting in the potion getting all the hair off him. He raises his shoulder, before he doesn't have any hair anymore, and there is no hair on his shoulder.
Justin's shirt changes from the park, where it is a checked shirt, to his house, where it is a striped shirt, and again from his house to the park.
In this episode we are told that if someone kisses a werewolf then they will turn into one as well (which is how Justin turns into a werewolf). However, in later seasons, when Alex Russo starts dating Mason (a werewolf) she never turns into a werewolf, even after they do kiss. This is actually explained when they're talking to Mason about it, he says that this effect only applies to "mutt" werewolves. Purebred werewolves such as himself do not have this limitation.