Ears are down, eyes are dull, coat may be greasy and/or unkempt. Activity level is low.
Another issue that owners will encounter (and you will see) is staining. Adult gliders begin to show staining on their fur for several reasons:
1) Long term use of a less than ideal diet
2) Unclean living/sleeping conditions.
Staining will appear as brown, orange, or yellowish tint to the fur, especially to the areas that should be white (belly, etc).
The gliders below show staining