The incident occurred on Jan. 11 evening, and Nguyen Van Duy, owner of a spa on Hang Gai Street, noticed the two arguing with the vendor about price while checking his security camera.
Duy immediately questioned the vendor and reported to the police.
A conical hat typically costs VND40,000-70,000 (US$1.52-2.66) in that area, he said.
"I've worked in tourism in the Old Quarter for 20 years, and so I couldn't ignore this."
On Jan. 12 the police said they had summoned the vendor, identified as Nguyen Thi Thu, for questioning.
Thu admitted to charging VND250,000 for the hat.
She told police that after Duy intervened and asked her to lower the price, she reduced it to VND150,000, but the tourists refused to buy.
Thu acknowledged that her action could negatively affect Vietnam's tourism image and apologized to those involved.
Camera footage shows a street vendor returns money to foreign tourists after they refuse to buy a conical hat in Hanoi.
There have been several recent cases of tourists being gouged in downtown Hanoi.
In July 2025 a group of Filipino tourists paid nearly VND1.4 million for a taxi ride of less than one kilometer in Hoan Kiem Ward, 50 times the normal fares.
In September 2025 an Australian family was charged VND1.2 million for a cyclo ride, three times the regulated fare.