When clients don't pay...

If the check I write to pay off my credit card bill/cell phone bill is even just one day late, they tack on all sorts of penalties.

I don't have a policy regarding penalties for clients who think it is cool to be late.

Maybe I should create one and stamp the following text, in boldface, in all my invoices: You must pay this bill when due. If you foresee your check being late, please contact me. Failure to do so will result in a 10% penalty.

Certainly it is more professional than the alternative: Pay me, you vile fiend!