Scams are everywhere. Terrible breeders are everywhere. How do you know if you can trust a breeder, especially in a world where most Puppy Sales are done online?

Google Them. Complaint Boards, BBB, Etc. can help point out some bad breeders. However, a breeder can easily change their business name to escape their bad reviews, so watch out for this. On the other hand, if you can find tons of positive reviews and a great following this is a good sign.
What Photos and Videos are you sent? Are they stock photos? Or only photos in front of one backdrop? Can you see any evidence of how and where the puppies are raised? Your average puppy mill today will have their puppies living in filth, but then every couple weeks have them bathed and fluffed just so they can get photos to sell them. If it is unclear how a puppy is being raised, then that is a Red Flag. Instagram stories are a great tool used today to show how puppies are being raised.
On this same note, do not think a breeder that does not allow random home visits has something to hide. How would you like it if someone different came to your house every day to just have a look around? However, the Red Flag would be if a breeder refuses to let you visit and see where the puppies are raised even when you are there to Pick Up. If the breeder is adamant about meeting Off-Site, Red Flag.
No photos of the parent dogs online. If a breeder does not have the moms and dogs listed on their website there is a reason.
Do they give you a bad feeling in your gut? Trust your intuition. If they seem slimy or scammy, just find another breeder. I have also had experiences with a lot of them that are just mean and rude, and if I am saying that then they must have been bad.
They are not knowledgeable about genetics, grooming, canine nutrition, etc. When you are spending thousands of dollars on a puppy you want to find a breeder that knows what they are doing and has put a lot of effort into their program. If they do not know the basics and are not growing by learning, then find another breeder.
And most importantly, the Red Flag of them not being passionate. Do they love what they are doing? Do they love puppies or just see them as a source of income? A passionate breeder is going to put that passion into their program and it will show.

If you have hesitations about a Breeder, just keep looking and find a different one. If you think you are getting a “Great Deal” on a puppy because they are half the price of all the other breeders just know there is probably a reason for this.