“非法买卖的”可以翻译为“illegally traded” 或者 “illegally bought and sold” 。
“illegally traded” 强调交易行为本身的非法性。例如：The illegally traded artifacts were eventually recovered by the police.（那些非法买卖的文物最终被警方追回。）
“illegally bought and sold” 更直接地表达出“非法买卖”这个动作过程。例如：We should crack down on the activities of illegally buying and selling wildlife.（我们应该打击非法买卖野生动物的活动 。）