Tourism Minister Zoe Bettison said the event was the "new way of marketing" and the cost to the government was much less than the $1 million suggested by the state opposition.
But the opposition said it was outrageous that taxpayers were forced to foot the bill for the event that was attended mainly by social media influencers and celebrities.
Smith appeared at the McLaren Vale concert on January 11. It was attended by about 300 people, including 115 who won tickets through interstate radio station promotions.
Others in the crowd were media identities and social media influencers.
Ms Bettison said commercial arrangements prevented the government from disclosing the cost of the event and how much the singer was paid.
But she said the cost was "a lot less than the $1 million being proposed".
"This is the new way of marketing," she said.
"We've got to go out there and do things differently. We want to turn people's heads and see South Australia as a place to visit.
"I certainly think that this concert and Sam Smith being in South Australia has done exactly what we wanted to do."
But opposition tourism spokeswoman Jing Lee questioned the government's lack of transparency.
"Because (Premier) Peter Malinauskas won't reveal the details of the secret Sam Smith deal, we have no way of knowing the positive benefit for South Australia – and that's if there even is one," Ms Lee said.
"We support events and big names visiting South Australia, but there needs to be a benefit to the state and the community.
"There are also concerning rumours that celebrities and influencers were forced to post a pre-determined amount of content on social media platforms to make the concert look like a huge success."
Ms Bettison said when tourism officials targeted influencers for promotions, they looked for diverse individuals with a significant following.
"I think they have a protocol that they follow. It's not only just about the amount of followers and posts, it's about the interactions with those posts as well," she said.
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