Me: “Here’s the invoice for £400, thanks”

Client: “Ok, thanks.”

Three Days Later… 

Me: “You only paid £300, I think you probably made a mistake?”

Client: “I know, I gave myself a discount.”

Me: “I never gave a discount?”

Client: “Well, we won’t be using the design anyway.”

Me: “Please complete the invoice, people do not do business this way.”

Client never paid up.