I will give some info on what I learned from a Customs agent I used to speak with on occasion. He told me that known places that distribute aas's from out of the country are red flagged in their system. From time-to-time they will randomly search packages from these places. Larger packages are searched more often than small. If a small quantity of aas's are discovered, they will document the incident, and most of the time let it go through (depends on the quantity). If a person (or destination) has received 3-4 shipments over a period of time (unknown how long of a period), they will make an inquiry with whatever local law enforcement agency the location/person is in. Sometimes they pay a visit, sometimes they don't. It all depends on their case load at the time, the amounts of aas's they are dealing with, or if their admin wants a "crack down" and make some "examples" out of the purchaser so it can be advertised in the news.
If you are getting aas's from another country, you can almost be assured the place is red flagged. It's just a game of percentages being played whether you get caught, or receive your packages. Just follow advice given from those who have "been there and done that" and one should be fine.
This is just some info from one Agent that shared this with me. This was a few years ago and things may have changed from then till now.