It will be a help to write a brief description of the area rug and its condition, check the back and front for stains, worn and discolored area, moth damage and other abnormality that you can see.
Take photo of the whole rug so we can see the whole. For large rug divide the rug into three section and take a photo of each section.
Fold the corner of the rug like above photo and take a photo of the corner from not more than 3 feet distance, we need to see the back of the rug, the rows of knots and the corner fringes of the rug.
Sides of rugs get worn as they are used, check the sides and take photo from the worn areas, like above photo. As we can see the traffic area stain and the worn knots clearly.
Used rugs usually have stains on them, the back and or front of the rug. Take a sharp photo form these areas. Like above photo.