They use applications that keep them honed in how much of a product there is, what the average price is on any given day, etc. So when supplies tighten, they raise prices.
It's why prices can be all over the place. When I buy ink for my printer, sometimes I wait days, waiting for the price to come down because it can fluctuate like $10 a drum. I tell my husband all the time he's getting ripped off. He doesn't care though-he's a online shopaholic and a convenience shopper. (:
Hubby and I have used amazon for over 20 years now. It was ‘convenient’ and ‘new’ way back when. Now it’s just amazon. I’ll pay a cpl bux more for something somewhere else just because I don’t like bezos.