Sentence:  The merchant importers ... endeavour, as well as they can, to suit their occasional importations to what, they judge, is likely to be the immediate demand. With all their attention, however, they sometimes <WSD>over-do</WSD> the business, and sometimes under-do it. 
Meaning of the word marked with <WSD> tags:  To do too much; to exceed what is proper or true in doing; to carry too far.