Does selling on Marketplace count as income?

Could you please clarify if the proceeds from selling on a Marketplace should be considered as taxable income? I understand that cryptocurrency transactions can be complex, and I'm trying to ensure that I'm compliant with all relevant tax regulations. Is there a specific threshold or criteria that determines whether a sale on a Marketplace should be reported as income? Additionally, how does the nature of the transaction - such as whether it's a one-time sale or a recurring activity - affect its classification as income?