If your quick bread has:
A cracked top: A cracked top is desirable and not a fault.
Tunnels and voids: Tunnels and voids in the bread are a symptom of over mixing. Mix only until the dry ingredients are moistened. Some lumps may remain.
A tough texture: A tough texture instead of a tender texture is another symptom of over mixing. Occasionally, too high of baking temperature will cause toughness.
A soggy texture: If the batter is left for too long before baking, it may be soggy or sunk in the middle. If the there is too much liquid or not enough leavening, the bread may be soggy.
A coarse, crumbly texture: The bread should be moist and dense. Too much fat or too much leavening will cause the bread to be crumbly.
A bitter, soapy aftertaste: Too much baking soda or baking powder will create an aftertaste.
Too thick or too brown of a crust: A tough thick crust may be caused by too high of oven temperature or too much sugar.
A greasy crumb: Too much fat will create a greasy texture.
Crisp edges: Too much fat or too much fat and sugar will create crisp edges.