If this purchase was an electronic one, it is possible that the authorize.net software did this. If the software is unable to get an approval quite fast (a matter of 4-6 seconds), it will often disconnect and try again. Unfortunately, the electronic traffic still goes to authorize.net, even if the software disconnects. Depending on the traffic at that at the ACH (all cards, no matter which type, go through a clearing center. The ACH clears cards for North America), the card gateway could have the attempts set "high". A telling sign would be the exact times of the attempts to authorize. I bet they are all within a matter of 60-70 seconds.
Phil Ellis
Phil Ellis