mark

翻譯研究：美國的俗語中，mark有嗜好；老好人，易受欺騙的人；施錢[食品]給無業遊民的場所等意思。（參考微軟的Word字典。）所以這段話裡面的unsuspecting marks，應該是指「不知情且容易受騙上當的人」：

• This may have worked to some extent back in the days of Jay Gould and all the “stock jobbers” who could corner, overrun, or dump their stocks on unsuspecting marks, but the prospects for accomplishing it today are not good unless you like prison food.

參考：deception 瞞騙；欺騙；欺詐；爾虞我詐；受騙；騙局；騙人的東西