even when looking at the post history as its usually so short.
There are two possible hypotheses:
(1) They are farm accounts. Got promoted from minor merit abusements to move upwards to Junior Member rank.
Then, later they got banned due to plagiarism.
(2) They are real accounts (not farm ones): But, they simply tried making pseudo- / fake- quality threads to earn at least one merit.
Then, later they got banned due to plagiarism.
I don't see reason to sell Junior Member accounts. The most probable scenario is bans due to plagiarism.