I'd double check the identification 1st and foremost... Pet stores are not always experts regarding anything aside from taking your money. Post a picture here or at least google the species to confirm. Does the finder live where Chucks exist in the wild? It could have suffered unseen trauma from a car tire of course. Yellow flowers generally evoke a feeding response, especially dandelions. On the off chance it's something else try a "super worm" presented on the cage floor to see if that brings about a feeding response. Room temperature for humans is anything but stimulating for a rock basker... so insure that the background temperature is more than 80 degrees.