She says adopting a "farmed" puppy can be dangerous if it has not been socialised properly.
"I have clients where, judging by the overall temperament and behaviour of the puppy, I am very suspicious about where the animal came from."
Ms Voss says most people meet the breeder at a "halfway location" to pick up their new pet and never see the dog's previous home.
Auckland SPCA's chief inspector, Nick Thomason, says staff monitor Trade Me to try to identify those involved.
"We look for red flags if we think there may be farms operating," he says.
Ms Kalin says many people are thinking only of the money.
"There is no need for society to be in the business of breeding. The public can't be confident, whether it is selling or giving away online, that due diligence is being exercised in terms of the animal's welfare."
She says the internet is also contributing to an increasingly flippant attitude towards ownership.
People no longer consider it as a 12-year commitment because if it "doesn't work out" they can just put the dog back on Trade Me and maybe even make some money.
A review by The Aucklander of Trade Me listings shows dozens of dogs being given away, some only months old, with owners citing a change in circumstances.
Chica, a 2-year-old rottweiler cross staffordshire bull terrier, is being given away because her Auckland owners don't have the time anymore.
"Despite having the best of intentions, Chica's existing owners work too long and hard to give her the attention she deserves and needs," the listing reads.
Ms Kalin says sometimes people cannot keep pets for legitimate reasons but before adopting they need to seriously consider if they will be able to provide the necessary care for up to 12 years.
Nothing proves this more than staring into the eyes of cute 10-week-old labrador puppy Kandi, who was dropped off at the SPCA shelter after just two weeks when the owners realised they didn't have enough time for her.
Standing in front of Kandi's cage, Ms Kalin is visibly upset. She says she doesn't know why the owners didn't consider this before adopting a puppy they were in no position to care for.
"Some nights I have gone home with tears in my eyes thinking of the poor animals' backgrounds."
She says she would like to see every animal that's not owned by a breeder de-sexed before it can be sold or adopted.
She understands that the SPCA cannot stop online adoptions but says the organisation will continue to educate the public on the risks involved.
Ms Kalin say most of the time people are completely unaware of the risks, including the large number of animals that are not de-sexed, micro-chipped or vaccinated. Animals sold online may also have underlying health and temperament issues.
"You won't know if there is the presence of genetic defects," she says.
"People may be adopting animals with significant health issues that aren't immediately obvious."
All SPCA dogs are checked for defects and health issues, micro-chipped, de-sexed and temperament-assessed before they are adopted out, and that's what the $260 covers.
The SPCA also offers to cover any costs for undetected medical issues during the first two weeks.
It matches dog breeds with new families to give them the best chance at looking after their animals. "You wouldn't give a first-time owner a husky puppy, even though they are probably one of the cutest, because they are extremely high-needs dogs," says Ms Kalin.
Campaign and data manager Vanessa Eggers says the organisation has begun listing its dogs on Trade Me to try to compete with online sellers.
"The goal is to interrupt people from making what could be a bad choice and redirect them back to the SPCA.
"We want to increase our adoptions at the expense of these other 'breeders'."
