This is the most important part of getting great shirt fit. The seam should sit exactly where your shoulder meets your arm. Can a tailor fix it? NO
Proper sleeve length ends at wrist. Should be slightly longer than a casual shirt, so that you see some cuff when you’ve got a blazer or suit jacket on. Can a tailor fix it? Shorter, easily. Longer, no.
Slim but not tight through chest. Just like the shoulder, you want the fabric flush with your skin, without pulling or creasing. Can a tailor fix it? Afraid No
No ‘muffin top’ around waist (clean tuck). It should fit flat against your stomach without any bunching or pulling. Can a Tailor fix it? NO
Neither tight nor billowy; should allow for natural motion. Can a tailor fix it? A big no.