Dealer listing sham cars for sale on CarGurus

I am in the market for a car for my daughter. I have
been looking on CarGurus. Since I have already
used CarGurus to previously buy and sell vehicles, I
am fully aware of the process involved. Saturday
morning, I found a car in NJ that I was prepared to
make an all cash offer on, which I did. The dealer
salesman and I both agreed on a cash price, after
he had the offer approved through his sales
manager. I supplied the dealership with all my
personal information needed for the sale. He
stated he would process the sale on Monday. After
hanging up with him, he called back within 5
minutes to inform me that, unbeknownst to him,
there was a buyer on the lot holding the keys, and
he could no longer sell me said car. I told him
thank you for his efforts and hung up. I went on
searching for cars over the last 2 days. I have
noticed that said dealer still has the car listed on
CarGurus, but I was specifically told that car was
sold, and I could not buy it. I'm wondering what
protections CarGurus offers it's potential buyers
from being scammed by (so called) reputable
dealers. If said car was truly sold by this dealer to
an individual physically present on the lot, why
would said car continue to be legitimately listed on
CarGurus? I believe I haggled said dealer into a low
all cash offer, that they had decided they were not
happy with, and as a result made up an excuse to
cancel the sale we had agreed upon. Is this
acceptable sales protocol? Is this behavior
acceptable to CarGurus?? If so, I will no longer use
CarGurus for my car shopping needs, and will
spread the word to all I know of the kind of funny
business taking place on CarGurus. I expect an
answer as to why this behavior can, and does,
happen on CarGurus. I am a very upset customer.