Earlier quoted context omitted.
In my experience, the larger the organisation, the longer the presumed payment terms. I've learnt to demand payment in advance, otherwise I'll get caught up pos-hoc in the labyrinthine and entirely cloistered whims of accounts departments who seem to think they're morally-placed to dictate whatever terms they wish. Worst in my experience was Unilever, who simply assumed they could pay in 90 days, which ..er.. rankled…
i've read comments like this before on hackernews. Are the payment terms not on the contract signed? It seems like something you'd really want to understand before starting a project...
I tend to disagree with that mentality.