On top that, offer a 5% discount if they pay within 30 days. Helps with a lot of accounting departments.
Charge another $5/10 an hour if you want to compensate.
I once onboarded as a vendor for a large, inflexible client and had to choose between two possible payment terms.
something like: EITHER Net 90 OR a schedule of discounts for any payment earlier than that (e.g 1.5% for 30 days and 3% for 15 days). and I wondered how many of their vendors simply jacked up their rates or fees to compensate, thus saving the inflexible client nothing. I guess this is very common.
Invoicing an engineering manager who needs things to happen tends to be the least friction from my side.
Even if it costs more on the purchase, inflexibility does help streamline business operations. Any business who can just mandate "this is how this process is going to work" and make it stick is going to benefit from not needing to make bespoke agreements with every little vendor they co-operate with. I believe WalMart is the classic example for this case.