I do not think it is ever a mistake, it happens too often now to be called a mistake. If it were also a mistake, then you would have also experienced vendors paying excess, but no, they are always paying lower than what they should.

This particular scam method dey vex me ehn, and i don encounter am a few times. For business wey person dey do, still dey make profit, you still dey find way to scam your counterparty, e dey very sad that there are people like this.