Yes, I really am left-handed.
The thing about drawing realism (or at least trying to) is this: when something isn't right, everyone notices and they notice it immediately.
When someone orders a custom portrait from me, I send them scans of the drawing in progress and ask for suggestions. Often the customer will show the image to family members and consult with them, then return with a comment, such as "her smile needs to be wider," or "his eyes are too small." Next, because I have very sweet customers, they will usually follow that up with an apology for their supposed impudence: "But really, you're doing a great job! You're the artist, so I'm sure you know what to do! That was just my two cents. So sorry to be so picky!"
Although usually I love to hear people insist that their opinions are inferior to my own, when it comes to drawing I have learned that it's best to listen to people's feedback. It doesn't take an artist to notice a difference between a photo and a drawing. My little brother, who is still at a stick figure level of drawing, used to critique my art with remarkably precise observations. People can just tell - especially if it's a drawing of someone they know in person.
Sometimes I impulsively feel annoyed when someone looks over my shoulder and points out my mistakes. But if I swallow my pride and take their advice, it always ends up improving the drawing. People can see things that I can't, no matter whether they're art professors or little brothers.