One of the reason that prices vary for the same printed map is that no two maps are identical. There are a number of defects that affect printed maps in varying degrees. Here are a few:
Centerfold. Most large maps when published in atlases were folded in half with a guard pasted to the fold. This guard was bound into the book and allowed the map page to lay flat without diving into the binding obscuring detail. The folded paper is weak, vulnerable to wear and easily damaged, particularly at the bottom. Many folded maps have splits to some extent and many have been repaired with varying degrees of proficiency. It is perfectly acceptable to have a centrefold on a map and it can be a good indicator of an urestored map.
Margins. The unprinted area surrounding the map varies greatly between publications, the 17th century Dutch publishing houses of Blaeu and Jansson for example, printed their maps with large generous margins but the small pocket atlases of the 18th century, in keeping with producing pocket volumes, often lacked an appreciable margin. Large margins protect the printed area of the map from nicks and tears at the vulnerable page edge including the centrefold. Margins may be reduced later in the life of the map as a result of trimming by the bookbinder in a rebinding or aesthetic preference by a picture framer.
Discolouration. Paper can be affected by many materials and substances. Atmospheric factors can affect any impurities in the paper causing browning or spotting (foxing) most usually on 19th century paper. Offsetting from the printing ink or early hand colouring can be unsightly. Early colour contained pigments that could adversely affect the paper, especially greens containing verdigris which are always a good indicator of original colour by the staining that can be seen on the back of the map but which in severe cases can destroy the paper completely. Inferior framing materials contain acids which can leach into the map, damaging the structure of the paper and browning the page - this can occur over the whole map when acidic backing materials have been used, but is also commonly found as a brown line around the map border from the inferior mount board. Framed maps can also be subject to fading, particluarly of the colouring if exposed to sunlight or UV.
General damage. Tears, splits, nicks holes, scuffs, creases and buckling are obvious defects, the area of the map affected can be important - in the margins, outside the printed area they may be unimportant but on the printed area affecting topographical detail or decorative elements similar damage can be significant. Some creases can be termed "printers creases", these are accidental creases made in the damp paper prior to printing.
Restoration and repairs. It may seem incongruous to have restoration and repairs under the heading of defects but ideally maps are best unrestored and frequently repairs are carried out by less than able hands causing greater damage than the original fault. Small tears are often repaired with acidic adhesive tape, splits joined misaligned, maps overcleaned (bleached) and commonly pasted down to board to flatten the map for framing.