Well it varies a lot and depends greatly of the stature of the parties.
When I was a small wholesaler I offered 30 day terms to most of my customers, the tiny guys would either pay right at 30 days or need to be chased endlessly. The medium guys were similar although some might say they cut cheques only once a month so the payment might come a bit early or a bit late. The big boys were usually the worst, some would say "we don't care what your terms are we never pay faster than 60 days, take it or leave it".
Lots of variation with the bigger companies, some were very accommodating (HMV/Sunrise) while others were just awful (Sams). On the other hand in terms of headaches induced the medium size customers were the worst, they usually made lots of unfulfilled promises and were the ones who would say "sure you can come pick up a cheque" but on arrival would explain "oh sorry, Bill the controller left early and didn't sign your cheque"
Had a few customers who simply would not pay in less than 120 days, you want the order you accept the terms or bugger off.
There are no hard and fast rules in the wholesale game unless you have a product in such demand or limited supply that you can dictate (and enforce) the terms. Schmoozing can work, I had a number of customers who paid me much faster than they paid their big suppliers simply because they could empathize with my situation.
Of course the norms vary from industry to industry.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
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