I am not a lawyer...
I'm no lawyer either, but there probably won't even be an investigation if they found someone doing this.
However, it could be seen as tax fraud/tax evasion and could be prosecuted as such (assuming your local police force has resources to do so). However, if you stay on PGP and encrypt your messages, it will be hard to actually get any proof for their case, unless they seize shipments of the product you are trying to sell or something similar (but if the item isn't illegal in itself, the post system will have no reason to seize it).
Anyway, there's always Open Bazaar as an alternative. Not sure how active that place is at current moment, but you might get something sold.