Generally, these tiles are removed during sorting and grading before they are packed.
If a few were to slip through the process, they are not to be installed. The unmarked area of the tile is sound and quite suitable for using as a cut tile, but the damaged glaze makes it unsuitable for a whole tile to be laid.
If a few imperfect tiles have been laid, especially with firing cracks, they should be replaced by the tiler before the job is finished.
If the tiles have not been laid, call the Beaumont Tiles branch where you purchased the tiles and they will arrange to exchange or credit the tiles for you.