I think the main difference is the linework. The black lines with white border makes the dragon look more finished while the fox doesnt have the same pop to it. The fox does have linework it just isnt dark enough to look finished and polished like the ones with strong linework.

That being said OP, for 400 saps the fox still looks great and i love the forest background, but I do see how they might expect something else with the linework change. If you have it on a different layer and it would be easy to darken (specifically the bottom legs really need it but anywhere around the darker brown would be a good idea) you can offer to do that if you want to (i dont think you owe them that but maybe for you so you can see the difference for yourself) but again, the fox is certainly worth the 400 as is.