Residents of the city have complained of new government measures to keep the festival, during which thousands of dogs are expected to be killed and eaten, low key.
Animal rights activists this month handed Beijing authorities a petition with 11 million signatures protesting against the festival, which they say is cruel.
An online petition on Change.org has attracted a further 2.5 million signatures, with a crowdfunding effort raising more than $110,000 to buy the dogs for sale and provide them medical care and new homes.
Yang Yuhua, an animal rights activist, flew to Yulin from the southwestern city of Chongqing to buy dogs sold at the festival.
“Dogs are man’s best, the most loyal friend. How could we eat our friends?” the activist asked.
Yang spent 1,000 yuan ($150) to buy two caged dogs at the market from the vendor.
Several others also dug deep, with the small number of dogs on sale at the city’s central market all bought by activists rather than locals.
Vendors said they hoped for good business this year, with “a lot of people” enjoying eating dog meat.
“It’s your habit, it’s my habit,” said a vendor surnamed Zhou.