All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Wearing amulets could be a minor Shirk or a major Shirk depending on the belief of the one who wears them.
In all cases, it is neither permissible to sell amulets that involve Shirk, nor help others sell them.
Whoever sells them or helps in selling them, by guiding people to the place they are sold in, and the like, while knowing about them, then he has indeed committed a sin.
Hence, he should repent to Allah by regretting what he had done and being determined not to do that again.
Whoever repents, Allah accepts his repentance.
However, merely selling these amulets does not render the seller a Kaafir (non-Muslim). It is not correct to say that helping someone to commit Kufr while not approving of it is Kufr. Rather, it is only forbidden, unless the assistance is accompanied with the approval of Kufr.
For more benefit, please refer to Fataawa 28531, 85125, 91549, and 262186.
Allah knows best.