Tannerite is, though. (And where it isn't, blasting charges for mining are. And where those aren't, fertilizer probably still is. Explosives are hard, yet also far easier than you'd think)

You'll find that regular fertilizer has explosion retardant additives. Which made me think (and was confirmed later) that the Beirut explosion was 'weapons grade' ammonium nitrate, rather than the stuff sold to civilians.

For instance; https://pubs.acs.org/doi/abs/10.1021/cen-v073n022.p006

Buy those things and you’ll end up on a list and under surveillance quickly.

Doesn't that imply you're already under surveillance? The list that we're on is: anyone who is alive and can be surveiled.

No, but there are specific collaborations for high risk purveyors of things like explosive precursors.

If you show up at a farm store to buy certain fertilizers in unusual quantities, that interaction will likely be reported or otherwise flagged.