What are best practices in checking out whether a webstore checkout is working properly or not? We recently set up a customer with the complete Netsuite including a webstore using advanced website builder. This has mostly worked out fine but there have been a few problems, one of which we are unable to fix because we are unable to see where the problem is coming from. I am posting this here in case someone has already experienced this problem and can tell us how they fixed it.

A customer goes to purchase something in the webstore and everything goes fine until they submit their payment. For most customers this goes as expected. However, for a few customers (about 5-10 transactions per day) there is a problem in which a customer gets an error message (which I don't know because I have not seen it) but I get a message as a recipient of a checkout error problem set up in SETUP > Setup Website > Setup Website > Shopping cart.