"In many EU countries the sale of SN to individuals is banned, but that doesn't mean buying if from abroad (importing) or the posession of it it. Every EU country indeed has it's own laws, but even if posession/importing happens to be illegal, buying such small amounts wouldn't result in anything worse than a fine in a country like Austria. What "dangerous substance" did this person import/purchase?
I can assure you, you won't get into trouble when buying from the Czech seller for the very simple reason it will get shipped in a truck which just drives over the open EU borders into Austria. No customs involved at all.
The only scenario where you possibly could get into "trouble" is when the Czech seller has to stop selling and the police asks him to supply a list of buyers because there are too many related suicides. It's an unlikely scenario and this could maybe result in a sort of "welfare visit". If such thing ever happens I can tell you we have the same problem since I bought SN from this seller as well."
search sellers outside country you reside simple as