On 9 March 2021, the National Revenue Agency (NRA) published its position on the application of e-commerce taxation for personal income tax purposes. The NRA stated that no personal income tax is due when an individual sells personal items and items that are not bought for the purpose of being resold immediately afterwards.
When an individual is regularly selling goods, which are clearly not acquired for private use but for trading and profit purpose, then they must declare the amounts in their tax return and pay the tax due.
The full text of the clarification, issued on 9 March 2021, is available here (in Bulgarian only).