You might want to ask about the purpose of the photo. If its for a label in a nursery that is one thing, but a catalog picture should get more. And you might ask for photo credit if that matters to you. Oh, and ask about exclusivity. You might not want to lose ownership of the picture. You might consider getting free product in return. Lots of possibilities...
On the other hand, if it was just a good picture and you aren't in the photo business, you might want to just take the money and run, LOL!