How is the frog doing? First week or two in your care will determine lot's about the future of this improperly cared for animal. At this time recommend dedicate your energy to helping frog and learning as much as you can from experience, so it does not happen to you again. It's better to pay regular price for a healthy animal, than get a malnourished or sick one for sale price.
We should all learn that no matter how much we want an animal, if seller is not caring for them properly it's time to walk away. Buying them because of desire or pity will only keep the seller business afloat and the abuse on other animals that replace it will continue. Good luck
!