hey there! <3 here's the answer, pulled from the
Terms of Service- You may only sell your Kotashika for equal to or less than the amount you paid. If obtained through a trade or other non-monetary exchange, the design may not be re-sold.
a kotashika that was purchased can be sold for the total cost of art + original sale price! ^u^ If it wasn't purchased, then the kotashika can only be traded/gifted.