The ironic part is that the clients that don't need the looser payment terms (more time to pay the invoice) are the ones that get them

Kind of mirrors "it's expensive to be poor"

I took "good client" to mean, "is easy to work with/communicates well/knows what they want", not just "pays on time". The inverse being, the ones who don't pay on time were already a pain in the ass to work with.