With larger mirrors, check that the glass doesn't warp the reflection. To test this simply stand at a reasonable distance from the mirror and view your reflection. If you notice a warping effect then there is a flaw in the glass. Note however that there is always likely to be warp at a distance greater distance particularly with larger mirrors, so use your judgement to decide if the quality is of an acceptable level.

In order to make a mirror, the glass must go through a process known as silvering where one silver is applied to one side of the mirror in order to create the reflective surface. If there are black marks on the lines or glass this may mean that the silver has been scratched on the inside surface of the glass. Too large a scratch may ruin the mirror.