Working With The authorize.net Server Integration Method (SIM) Payment Gateway, Part 1
Example 2: Poisoning the order_total_input Variable

You can select any options you like in the form below, and the display total will be correct.
However, once you submit the form, the order_total_input hidden input's value will be set to 0.01, no matter what options are selected.

Choose a membership level:

Annual banquet tickets:

Would you like to purchase a T-shirt?

Your order total: $0.00

Example 1: A Form That Computes Order Total Via JavaScript
Example 3: Using JavaScript To Change Individual Order Options
Blog entry: Working With The authorize.net Server Integration Method (SIM) Payment Gateway, Part 1: Don't Use JavaScript