Even with photographs, online buyers need to exercise some caution.  Most online listings only provide one photograph, and although with proper camera technique it is possible to photograph most of the book or dustjacket with one snapshot, most online photos do not show all angles of a book.  In such cases, it is essential for the seller to clearly indicate any condition issues or damage not clearly shown in the photograph(s).  The rule of thumb is that there should be no unpleasant surprises, or (conveniently) overlooked issues to disappoint the buyer.  Be wary of photographs that may omit damage (i.e., a nice photo of the driver side of a car, but none of the dent on the passenger side -- or a photo of the front of an antique glass piece, but no photo of the crack on the back of the piece, etc.).  Any potential buyer would obviously be disappointed when buying online only to discover these omissions after the fact when they open the mail.  Conscientious sellers should never put buyers in this position.

Grade

10 Point Book Grading Scale with Condition Details

Mint (10)
/As New
(MN)

Reserved exclusively for new books, fresh off the press.  Absolutely no blemishes, and preferably shrink-wrapped. 

Note that most new books from the bookstore are no longer mint, as they often shows signs of handling.

Near Mint (9)
/Very Fine
(NM/VF)

An extremely attractive copy with great eye appeal. Moderate to high cover gloss. If held at arms length, a book in this grade would appear to be flawless at first look, although upon closer scrutiny it will lack the fresh, crisp look of a mint book. 
Book should have no defects -- no discernable wear or rubbing, no fading of the spine, no dog-eared page corners, no bumps, rubs, sunning or foxing to the book.
Spine may have a couple of small stress lines and may show mild signs of handling upon close examination. A small 1/4 inch crease at the corners is allowed.
 

Dustjacket should be almost "like new" with no tears, chips or fading, and only very minor signs of use, no discernable wear or rubbing.

Fine (8) (FN)

A very attractive copy that shows minimal wear.
Book is clean with minimal defects. Binding and hinges are tight. 
Corners are sharp. 
Pages are clean and free of any writing or bookplates, toning should be minimal.

Dustjacket should be nearly crisp.  There should be NO edge chips.  If present, closed tears should be under 1/8".  There should not be any trace of fading or sunning to the book or dustjacket spine.

Near Fine (7)
(NF)

A nice, collectible copy that shows mild wear.
Book is very nice with very minor defects. Binding and hinges are strong. 
Corners and edges may show only mild edge rubbing. 
Pages are nice, perhaps some writing in pencil, toning should be creamy white to mild yellowing.

Dustjacket should be fairly crisp.  There should be minimal edge chips (< 1/8") NOT affecting lettering.  If present, closed tears should be under 1/4".

Very Good Plus (6)
(VG+)

A nice, collectible copy that shows light wear.
Book is very nice with minor defects. Binding and hinges are firm. 
Corners and edges may show some rubbing.  Any soiling must be minimal.
Pages are nice and supple with no brittleness, some writing in pencil or a nice bookplate, toning should be creamy white to somewhat yellowed.

Dustjacket should be attractive.  There should be only minor edge chips (< 1/4") NOT affecting lettering.  Closed tears should be under 1/2". Flap fold may show some minor friction.

Very Good (5)
(VG)

A good collectible copy that shows moderate wear. 
Book will show small defects such as minor darkening or fading to book spine, or minor creasing and soiling. Bookplate or inscription should be discrete. 
Corners and edges will show some rubbing or bumping.
Pages and interior covers may be yellowed to lightly tanned, but should be fairly supple with, at most, minor brittleness.

Dustjacket should be nice.  There will be some edge chips (< 1/2") which may affect lettering.  Closed tears should be under 1". Flap fold may have wear or closed tears.

Very Good Minus (4)  (VG-)

An acceptable copy that shows wear.
Book will show some defects. Binding is fully intact with edge rubbing. 
Corners and edges may be bumped and rubbed.  Hinges may be tender.  Pages are good, writing or an old bookplate, toning may range from yellowed to browned, paper may be starting to brittle. 

Dustjacket should be presentable.  There will be edge or corner chips (< 1") which may affecting lettering or design, and some long closed tears (< 2").

Good (3) (G)

A somewhat collectible copy depending on rarity. 
Book will show noticeable defects.  The hinges may be weak. 
The spine and pages may not be tightly attached, and there may be some damp stains or soiling; spine extremities can show minor chipping, corners can all be bumped.  Perhaps a dedication inscription of previous owner's inscription and/or stamp.

Dustjacket will often have edge and corner chips that remove parts of title or image.  There will be long closed tears or even open tears.  The spine will often be faded or darkened. s

Good Plus (G+) and Good Minus (G-) can be used to indicate slightly better or worse conditions respectively.  A book in Good condition shows average use and wear, but not in need of a replacement binding, not all tattered & torn, not with significant damp stains.

Fair (2) (FR)

Not really a collectible copy, usually just a reading copy. 
Book will have significant defects including perhaps hinge or page splits. There may be heavy dampstaining, excessive stains or foxing in the text, a very tattered cloth or very scuffed and rubbed leather binding with additional problems such as underlining in the text, lacking endpapers, both hinges cracked, heavy dog-earring of page corners — in general only a step above a reading copy and not a desirable copy unless you value content much more than condition

Dustjacket will have significant chips and tears.  The color of the binding and dustjacket will often be faded. 

A book in Fair condition shows much use and wear and multiple problems and/or defects and unless the book is very scarce or rare probably should not be added to your collection.

Poor (1) (PR)

Not a collectible copy. 
Book will have major flaws often including page tears, separated binding and other detractions. Book will usually look tattered and heavily worn, and may be partially disbound.

Dustjacket (if present) will have large chips and/or missing parts.