The phrase “no great shakes” means: Nothing out of the ordinary in proficiency or achievement; no particular bargain; nothing of importance or consequence; nothing to write home about; no prize.
Maybe, as suggested by the great Oxford English Dictionary, the ultimate source alluded to the shaking of dice, in which the turn is so often nothing more than mediocre.
But the expression was such common slang in the beginning of the nineteenth century that Lord Broughton, writing of an incident that occurred in 1816 (in his Recollections of a Long Life, 1865), recalled that, to quote him, “W. said that a piece of sculpture there was ‘nullae magnae quassationes,’ and the others laughed heartily.”
That is to say, the others present not only knew their Latin, but immediately recognized that, translated literally, it meant “no great shakes.”