We (enterprise buyers) would never agree to that. In all contracts I work on, there is a lengthy back and forth between lawyers working out the terms. Something like a premium fee if we are late on a net 30 payment would be a deal-killer. We know it takes a long time to process payments. I don't intentionally delay, nor am I encourage to delay - it is just that the wheels of SAP turn really slow.
This is one of the things where mathematics gives way to linguistic manipulations.
If you add a "late fee", it's a no go. But if you get an "early payment credit that will appear on your next invoice", it is ok.
Don't know if this is still the case, but for a long time, merchants couldn't add a "credit card fee" (even though they pay it at 2-3%). However, they could give a "cash discount".
