The reason for this was not only that there were differences between koka and washi prices but also that there was no end to the corrupt practices by kokushi (provincial governors) at kokuga and Zaichokanjin (the local officers in Heian and Kamakura periods), who imposed unreasonably low prices as koka on local residents, buying more goods than necessary so that they could use the surplus to feather their nests.
これは、估価と和市価格の乖離に加え、国衙の国司や在庁官人が不当に安い価格を估価として地元住民に押し付けた上、必要以上に買い入れてその余剰をもって私服を肥やすという不正が後を絶たなかったからである。