After looking to following set of 14 Mao poem stamps, to me Chairman Mao Tse-Tung, was writing poem as hobby.
Compare following 2 screenshots and you will be surprised the difference in the price of Mao Tse-Tsung poem stamps or Poems of Chairman Mao China 1967 stamps, Mao poem stamps of china.
One is selling as Replica or copy stamps or not real where as other is selling as if it is Genuine.
I compare both and to me it looks like it similar with nothing difference.
One is selling for $15 and one sold for $3550.