1. In case the original bill of lading does not reach the port of discharge in time for customs clearance before the ship arrives at the port of discharge, the seller shall agree to provide the buyer with a standard form of guarantee for the release of the goods without the original bill of lading. The seller shall agree to provide the buyer with a standard form of guarantee for release of goods without the original bill of lading, signed by the buyer at the port of discharge before the ship arrives. The shipping agent shall provide the necessary documents such as delivery note for berthing, unloading, customs entry and clearance. Guarantee only in the absence of permission to use the buyer's signature, so that the discharge can be carried out but will not be placed in the hands of the customer.

2. Do you know what DA means here?

This DA I can't guess and haven't seen before. I guess it means this

The buyer appoints a forwarder at the port of discharge, at a competitive DA (price)

If you know what DA is, share it.