I use Overstreet & own several grading guides.  I do provide front & back scans on anything over $10, some in the $5-10 range too, cheapies just have generic thumbnails.

Some grading notes:

With old or expensive books I will count the pages & check for interior defects, on dollar books not so much.

I allow detached covers up to GD, partly detached up to GVG (or VG if otherwise nice).  Centerfolds detached up to GD+, partly detached up to VG+.

Subscription Folds:  Any full length color-breaking fold usually means GVG but sometimes VG if the rest of the book is in nice shape.

Water damage:  Limits the grade to FN unless it's really small and obscure, anything larger than a quarter usually drops it under VG

Books in GD can be read normally, books in FR can be read with difficulty.  I'll drop the grade below GD if it's incomplete, has large tears, is badly warped, or has something gross like mold.