A well-designed logo can still look unprofessional if it's misused — stretched out of proportion, crammed against other elements, or placed on a background it wasn't designed for. A few simple rules prevent most of these mistakes.
Never stretch or distort it
Resizing a logo should always be proportional (locking width and height together). Stretching it in only one direction — a common accident when resizing in a hurry — is one of the most visible, avoidable brand mistakes.
Respect clear space
Every logo should have a minimum buffer of empty space around it, usually defined relative to a measurement within the logo itself (like the height of a letter). Crowding other text or graphics into that space makes the logo feel cramped and unintentional.
Don't go below the minimum size
Every logo has a size below which detail becomes illegible. A brand guide should specify this minimum explicitly, so anyone applying the logo — an intern, a print shop, a partner agency — knows not to shrink it past that point.
Use approved color and background combinations
Most logos are designed with a primary full-color version, plus a reversed (light-on-dark) version for dark backgrounds. Applying the full-color version on a background it wasn't designed for is a common, easily avoided error.
Don't recolor or add effects
Drop shadows, gradients, outlines or unapproved color substitutions applied to a logo after the fact almost always look worse than the original — if a specific context seems to need a variation, that should be designed deliberately, not improvised.
The short version
Keep proportions locked, respect clear space and minimum size, and stick to approved color and background combinations. These few rules prevent most of the ways a good logo ends up looking unprofessional in practice.