In most EU countries law, this one is also considered as "solid business", regardless if you are incorporated or not:

If you are running on a level with focus one some revenue, if you are doing it somehow regularly and if you have at least some infrastructure to look like you are a corporate (billing system, customer care or similar), then you may fall under corp rules, even if you are not acting as an entity.

>Don't sell stuff as a incorporated business. Only do that once you cross a certain level of revenue.

Are you saying to sell as an individual? People don't do that because if you ever get sued, it puts your personal assets at risk.