When considering the selling and buying of animals and animal parts, be aware that each state has their own laws concerning this. You need to know, not only the law of the state you are in, but also that of the person you are selling to or buying from.
There are also rules on individual buy/sell/auction websites of what may or may not be allowed.
Here is a small bit from the "Code of Virginia":
Code of Virginia § 29.1-521.
To hunt, trap, take, capture, kill, attempt to take, capture, or kill, possess, deliver for transportation, transport, cause to be transported, by any means whatever, receive for transportation or export, or import, at any time or in any manner, any wild bird or wild animal or the carcass or any part thereof, except as specifically permitted by law and only by the manner or means and within the numbers stated.
It does go on to mention that parts from legally killed turkey and deer may be made into things and sold, such as turkey callers, tools and utensils,etc.
Plant materials has a whole other set of rules. Most of the laws and rules are in place to stop the spread of plant diseases, bugs and to control "invasive" species.
Bottom line...do your research. (And, since I mentioned rules, remember the important rule is to always be nice.)