Rejection are of 2 types
1. Foreign country Government rejection.
2. Rejection by buyer - in actual its called not acceptance.
When goods are not sent as per the parameters of a foreign country then it could be rejected. One must get pre-approval lab test done from https://www.sgsgroup.in/ so that our products are never rejected by the government of foreign countries, generally developed countries like USA and UK have strong criteria but countries like UAE, Srilanka, OMAN, Qatar, Saudi Arabia, Bangladesh, Africa, Malashiya, etc does not follow any strict norms & generally accept all cargoes.
Rejection by buyer (non-acceptance) not visiting bank to collect documents in DP or DA & pay is a fraud, for it ECGC will pay you.