After you enter your credit card information, around step 4, chargesmart will sometimes add a "large payment security fee" in addition to the fee quoted when you enter you account number and the amount you want to pay at step 1. At that point, you can navigate back to previous steps using the "back" button without losing the information you have entered, so you can experiment with what happens to this additional fee if you were to pay different amounts.

I want to report some non-linearity in the large payment fee, so those of you considering using charge smart can know to try a do a binary search to see where your "large payment security fee" drops off. For example, here is some data for Pacific Gas and Electric when used with a Citi AA personal Visa (not a gift card), for which chargesmart charges a flat $7.95 per transaction plus the following "large payment security fee" depending on how much you want to pay (a 2.29% slope between $1000 and $2000).

$347.16 --> $0
$347.17 --> $4.95
$347.18 --> $4.95
$347.20 --> $4.95
$347.21 --> $4.95
$347.23 --> $4.95
$347.25 --> $4.95
$347.50 --> $4.96
$348 --> $4.97
$349 --> $4.99
$350 --> $5.01
$400 --> $6.16
$500 --> $8.45
$1000 --> $19.90
$2000 --> $42.80

Assuming that the "large payment security fee" is not a "bait and switch" sales tactic, then I guess the fee must somehow be dependent on information entered after step 1, such as the type of credit card being used. So, conceivably, you might be charged different numbers if you were to use a another brand of credit card such as MasterCard or Discover, or a debit card or a gift card.