Trading with Trade Manager question

Hi, I have enjoyed this server so far, thanks for the great work.
I have the question about the price when I try to sell fishes to the Trade Manager, in the same town, one day it becomes 30%, other day is 1000000% something, but when I sell them, it seems like my money doesn’t change (or maybe it was sold with low price).
Any suggestions and tips? I’m still a new player so.

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