Can you say "I am no expert", does it means the same that "non sono un esperto"?
Well, just to clarify, it has the same general meaning. But on a grammatical level, they are two different sentences, and "I am no expert," would not be a good translation of the Italian here. That sentence would be, "Non sono nessun esperto."
DL is cruel. I put, "I'm not an expert" and DL responded with "You are correct"
Because by writing un'esperto you are not contracting anything. When a contraction is needed the result is that less letters are written compared to the not contracted case.