“非法买卖的”可以翻译为“illegally traded” 或 “illegally bought and sold” 。
“illegally traded” 更简洁，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” 表述更具体，突出买卖这两个动作的非法性，比如：We should crack down on the market of illegally bought and sold wildlife.（我们应该打击非法买卖野生动物的市场。 ）