"买卖禁品者" can be translated into English as "those who trade in prohibited goods" or, more succinctly in certain contexts, "prohibited goods traders" (though the first option is more precise in conveying the act of trading).
"Those who trade in prohibited goods" clearly specifies the individuals involved and the illegal activity they are engaging in.
"Prohibited goods traders" is a more concise term that directly refers to the individuals who deal in prohibited goods, but it might be slightly less explicit about the illegal nature of their trade in some contexts.
In most formal or legal contexts, "those who trade in prohibited goods" would be the preferred choice for its clarity and precision.