Not necessarily -- if the first seller has it enabled, the second seller would just order it to be shipped directly from the first seller to the buyer, and never have it touch their inventory.

Fun story! A family member wanted to buy an air-fryer online. She found it on Walmart's site, then found it for $20 more on amazon. At first she tried to buy it from Walmart, but got frustrated with the process (setting up an account and stuff) and so she just went and paid the extra to order it from amazon. A few days later, she gets an air fryer in a Walmart box! At first she's super confused, and thought she'd mistakenly bought it from Walmart, so she went to cancel it from Amazon, and saw that that one had already arrived. What had happened was the Amazon seller was getting orders on their page, then immediately going to Walmart, ordering the fryer, then shipping it directly to the recipient. Kinda genius. Basically no overhead, no stock, just acting as a hidden walmart portal and pocketing a percentage.