Vendors meaning me the examiner.  Yes I have charged interest.  Your dentist or doctor does it on late payments why shouldn't we.  The few handful of companies I have recently done it to have paid it.  But of course they were companies I didn't have a vendor agreement package with.  They were clients I bill per search and our invoice states "Payment Due upon receipt.  Payments received after 30 days are subject to a 1.5% late fee"  It worked.  Yay for me!