One of the findings in the exam report that resulted in me getting hired here 10 years ago was a charge exactly $1 more than the actual FZD charge, not because of a vendor change but because of a price change that no one paid attention to. We had to go back to the date of the price change and refund the $1 for every one charged the fee from that date forward.
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The opinions expressed are mine and they are not to be taken as legal advice.