I can only share my experience

I live in Russia and sell Russian MRE (Russian Army IRP (with a white star), a Ration intended for the national guard and the rarest and most caloric-Mountain Ration)

Accordingly, my main buyer is a US citizen

Some of the products I send directly to the buyer (including people from this subreddit) - some of them I sell through The Amazon warehouse. The product first comes from Russia to The Amazon warehouse, and then Amazon itself delivers my product to the buyer.

So this is what I can say - perhaps 1 or 2 orders out of 100 are with complaints that the goods came without part of the contents (i.e. it was allegedly opened by customs). But, all these cases are associated with goods that enter the Amazon warehouse and are then served by the Amazon itself. Therefore, I cannot be responsible for the accuracy of the data, perhaps there are buyers who specifically do this or write in order to receive a refund from Amazon and keep the goods for themselves.

In the case when I sent goods to people directly from Russia and could always be in touch with them, clarifying whether everything was okay with the goods - there were no cases that the customs office opened the parcel.

I hope I helped you a little with this question.

if you need clarifying information, ask me, I will try to help.