It's not mandated anywhere in US law, but the vast majority of reputable retailers (e.g. Walmart, Amazon, Target etc.) have very generous return policies. They're usually far more generous than 14 days. As you might expect, there are of course reasonable limitations (e.g. customized products, digital products, etc.).

Amazon: 30 days https://www.amazon.com/gp/help/customer/display.html?nodeId=...

Walmart: 90 days https://www.walmart.com/cp/returns/1231920

Target: 90 days: https://help.target.com/help/subcategoryarticle?childcat=Ret...