WASHINGTON—A blue Louis Vuitton -style bag advertised by a Chinese merchant for $200 caught Andrew Carlson’s eye as he scrolled Instagram. And he knew he could buy it without paying the 25% tariff that President Trump put on Chinese handbag imports in May.

Since 2016, up to $800 in foreign goods shipped to an individual shopper in the U.S. are exempt from tariffs that predated the recent trade wars. The exemption allows consumers to avoid the shipping charge or higher price that American retailers often apply to recover the tariff cost.

It also gives an edge to Chinese sellers that ship directly to consumers in the U.S.—all the more so with the Trump administration’s trade action.

Mr. Carlson, a 25-year-old Los Angeles resident, said he was aware he was sidestepping tariffs when he bought his Vuitton copycat in July, but said he was simply operating under rules made by U.S. policy makers.

“It’s hard to not come off that I don’t care about bringing jobs back to America,” he said, “but I just don’t think that me not making this purchase is going to make a difference.”