Why there are two payment for one order with same remote ID Right now, I am using Commerce Paypal to capture payment. But I found there is a order which shows me two logs for capturing payment. However, I just find one in my paypal account and also I found the Remote ID in both two logs are same. 
The customer bought one item which costs $17, but the total shows on drupal is $34. What is the exact total price for this order? Does anyone know why this happened? Is there something wrong during my config?

Here is a screenshot for this strange order:
For some reason the IPN for that payment triggered the creation of a second payment transaction within Drupal Commerce. Couldn't tell you exactly why it happened, though it could've been the result the customer's page request and the IPN request being processed simultaneously. The module ought to filter out IPNs to not duplicate transactions like this, so if you see it again, file a bug report in the module's issue queue.

To answer your direct questions, the order cost $17, the balance is now negative (meaning it appears overpaid within Drupal Commerce, even though it wasn't), and it would be safe to delete one of the transactions (but you'd need to be logged in as an administrator).