The safest way is to ask the guests to pay in advance, but in that case, the risks of the guests will be great.

Letters of credit are relatively safe, but not absolute. If the market changes and the buyer decides not to buy the goods, he can pick out the discrepancies in the documents and refuse to pay, but there is nothing the Bank of China can do. Not to mention the collection, it is completely commercial credit, without any constraints. It is safer for both parties to pay a small deposit, such as 30%, and then let the guests designate personnel to inspect the goods after the production technology, and then pay the balance after passing the test.