"What for you are the giveaways that they are not native speakers?"

Their native language is the same as mine, so I presume I'm just sufficiently attuned to its sound to hear its influence peeking through. However, I suppose that the main giveaways for native English speakers might be the following ones in particular: No. 1 is mixing up several British accents, No. 2 puts too much emphasis on dropping the T and there is a certain Continental European hardness to her consonants, No. 3 devoices consonants at the end of words and her pacing might seem unnatural.