Little project for an insurance sales guy / finance coach / entrepreneur

My first thought: guy sounds extremely shady but ok let’s come up with a hefty price.

Guy accepts my offer and pays one third in advance as I asked. Of course he pays cash because he „didn’t make it to the bank“ but happened to have the big bucks in his wallet.

I give him a receipt for the cash payment.

Job is done I write an invoice for the remaining two thirds.

Guy transfers money to my account. No cash this time.
However he took the sum in the second invoice and subtracted the first one and 50 bucks extra and send the remaining entirely imaginary sum.

I text him. He does not get it and explains that he payed cash in advance.
I say yes but that is not the point. You can not make up the sums of your invoice yourself.

I send him three warnings via mail.

He sends an angry letter back sayingthst he payed one third in advance.

I tell him how nice it is that we agree in that regard but that the issue will go t court if he does not pay.

Sometimes I am fascinated how elaborately stupid people can behave. :/