If someone tells you "I don't lie" it doesn't mean they've never lied, therefore, it doesn't mean they will not lie. Saying "I don't lie" is in most cases already a lie, so you might as well remain skeptical and keep your eyes opened, because saying this could be a sign that they have something to hide.
Clarification: When I write, I don't prepare or organize my ideas, I just write what I would say if I was talking to you in person, so sometimes my blogs end up a little messy. I don't even proof-read what I write before posting it so you may find grammatical mistakes and poorly written sentences. Sometimes I'll read my blogs a day or two after publishing them and I may re-write things that weren't too clear and any embarrassing grammatical mistake. Also, English is not my first language, so I apologize if reading my blogs become a struggle. Of course, if this is the case, I would imagine you wouldn't continue reading.