Until a few years ago, traders would usually get paid within 30 days. To raise cash JAB lengthened payment terms to up to 300 days.
Finding financing to cover the gap has squeezed traders' slender margins.
"These guys have money, but they're not banks," says Oscar Schaps of INTL FCStone, a brokerage.
The banks lending to traders may take into account the financial position of their biggest customers.
So the traders' borrowing costs could rise if the roasters' credit standing were to deteriorate.
Big traders, such as Swiss-based ECOM or Germany's Neumann, face a less favourable balance of power.
They rely on the big buyers in a fragmented industry. JAB's tactics are compounding other problems.
Bumper harvests have pushed bean prices below $1.20 a pound, forcing farmers to sell at a loss. Traders are also struggling to cover costs.
Some could see their best staff leave. Andrew Kerr, a headhunter, says salaries are "starting to ease off" in Geneva, the world's centre for coffee trading.
One answer for traders may be greater scale. Consolidation would allow costs to be cut while increasing negotiating power.
More investment in storage, ports and transport would help them take greater advantage of arbitrage opportunities across the globe.
That should position them well to meet Asia's growing thirst for instant coffee.
Another strategy would be to capitalise on the trend for pricey gourmet brews that boast traceability and sustainability.
Small independent roasters have sprung up in richer cities. They are looking for specialist traders with direct links to farmers.
The dominant roasters have also woken up to high-end coffee. Nestlé paid around $425m in 2017 for Blue Bottle, a fancy Californian chain.
Supplying them with top-quality beans may be another way for traders to escape the grind.