I think the first talent, the most important talent, that liars should possess, is a good memory.
For example, your engagement over a chicken dinner, then it's outside and finally, although it was a huge surprise, a friend was on standby to film it.
The second thing is to be bright enough not to tell lies that can be contradicted and disproved.
For example, it is silly to tell a lie that The Archbishop will disprove a couple of days later. It is silly to tell lies when there are too many who know the truth.
It is silly to tell lies when there is ocular proof that will contradict you.
If you are a numbty, then a career as a liar is not for you. They have chosen the wrong career.
They are both numb. However, Megan scores over Harry because she is hard faced enough to brazen it out. If she were able to couple this talent with a good memory and selecting lies that couldn't be disproved, then she would be on to a winner.
Sadly, her lack of these talents mean that she has bared her arse in the window of John Lewis.