If you’re a donor interested in helping animals, the offer is intriguing. Give us money and we’ll use it to save dogs.

We’ll buy dogs to stop them from being sold by “puppy mills.” Your money will be used directly to buy dogs and won’t be used for overhead. Some of these nonprofits put the dogs up for adoption and charge people adoption fees of as much as $1,850 per dog.

Kim Kavin, author of The Dog Merchants, notes in this multi-page Washington Post piece that buying dogs from breeders is a surprisingly popular activity for nonprofits. She says that documents she “obtained from an industry insider” show that, since 2009, 88 nonprofits have spent $2.68 million buying dogs at the nation’s two government-regulated dog auctions, Southwest Auction Service and Heartland Sales, both of which are in Missouri.

While most of the charities buying dogs at auctions are small operations (entrepreneurs who raise money through GoFundMe and YouCaring), large and well-established animal rights organizations say that they don’t buy dogs directly from breeders.

The Humane Society of the United States, for example, maintains a list of “Horrible Hundred” breeders. The American Society for the Prevention of Cruelty to Animals has a “No Pet Store Puppies” list. People for the Ethical Treatment of Animals wasn’t quoted in the original piece, but in a follow-up story they said that these rescuers were “propping up the dog-breeding industry.”

The reason why the rescuers are buying dogs directly from breeders has to do with changes in the market for dogs. There are a lot fewer dogs coming into shelters than there used to be. Kavin quotes “one estimate” (which she does not specify) saying that the number of dogs killed in shelters has fallen from 20 million per year in the 1970s to 780,000 in 2017. If you’re an organization that wants to rescue a particular breed, they’re less likely to be in shelters than they used to be. So rescuers go to the two dog auctions.

What Kavin found is that there are a lot of rescuers clamoring for a limited number of dogs. She says that some of the older rescue groups have secret Facebook groups where they collude to limit how much they will pay per dog. But new entrants who have a lot of money and are willing to pay breeders often outbid them.

For example, in February an invoice showed that Jessica Land, who runs Dog Ranch Rescue and Lone Star Dog Ranch, paid $8,750 for a pregnant French bulldog. Land, like most of the rescuers discussed in the article, refused to comment. But a post on Facebook said that Lone Star had placed five puppies for adoption fees of $1,850 and then placed the mother for an adoption fee of $1,300. The group claimed that with medical fees they lost $2,421 on the transaction.

The highest price known to have been paid by a rescuer took place in a November 2014 auction at Southwest Auction Service for 130 Cavalier King Charles spaniels after an Alabama breeder went out of business. The auction proved very lucrative for rescuers; one person raised $188,815 on GoFundMe and another on YouCaring raised $157,955.

Most of the spaniels went to rescuers, but Will Yoder, a Cavalier breeder from Iowa, bought two dogs for $3,650 and $3,950. He said that as he was prepared to pay, a woman came up to him and said, “So, how much profit?”

“It was like, they hate me, and they assume I hate them, and she just walked up and looked at me,” Yoder said. He said the dogs were not for sale, but two hours later he called the auction house and said he would sell the dogs for $10,000 per dog.

The winning bidder was Angie Ingram, program director of Cavalier Rescue of Alabama. She spent $24,200 (including auction fees) on the two dogs, for which Yoder had paid $8,305. Ingram kept one as a personal pet, paying an adoption fee of $300, and the second dog was also placed for an adoption fee of $300.

As Kavin notes, about 280 cities and the state of California have banned so-called “puppy mills” from selling dogs to the public. But this shifts dog purchases from breeders who are regularly inspected by the U.S. Department of Agriculture to unregulated nonprofits.

Kavin’s article provoked many responses, ranging from the Agriculture Department declaring they had the right to license rescuers to asking the IRS whether nonprofits that use donated funds to buy dogs which they then keep violates charitable law.

Here’s a simpler solution: why don’t nonprofits that offer dogs for adoption state whether the dogs have been purchased at an auction? Most responsible breeders offer buyers background information on the dogs they’re selling, including health and genetic information that would alert a buyer to future medical problems a dog might have.

If nonprofits aren’t willing to tell buyers how they acquired the dogs they’re selling, donors should be suspicious—and ask what other information the nonprofit is hiding.