Import and export companies will sign "sales contracts" with foreign businessmen on your behalf, and you should also participate in the review of terms to reduce trade risks. Do you agree to accept the agreed delivery date and payment method? You need to confirm everything.
I wonder if the "factory" you refer to is your domestic supplier. If possible, you can sign the purchase and sale contract yourself.
About the letter of credit. Of course, it's for your import and export agency. They will pay you when they collect the money.