Most likely, it's been an intermediary bank charge applied. Pay attention to your local bank conditions for making payments, as most of the banks apply fees for providing their services that will be deducted from the transferred amount. Such fees may be either some fixed amount or percentage from your transaction depending on particular bank's policy. Thus, let yourself know about your local bank terms in advance to estimate your additional costs.
Some websites cooperate with certain banks or payment systems to make payment terms for their customers more convenient and faster. Please check if an auto auction company has any agreements with some financial institutions about free charge payments for its clients.