We cannot speak for our competitor "Pooprints" but typically DNA testing is extremely accurate. In fact, it is the standard in law enforcement and if the accuracy is good enough to put a human in jail, it is certainly accurate enough to fine a dog owner for not picking up their dogs poop.
Of course that all depends on the integrity of the process which is managed by private individuals in the field.
If proper protocols are followed and there is no cross contamination, the process is sound and reliable. But if the individual swabbing the dog handles 3 dogs in a row without gloves and DNA from all 3 dogs is mixed up, that is a huge problem.
Fortunately, if there is DNA from multiple dogs, the lab should be able to see that a sample is cross contaminated, so no dog is in danger of being confused with another.
However, it can be easy to mix up tubes at the collection site and having the wrong name on the swab when it is sent to the lab.
Mr Dog Poop solves this problem with individual kits that are packaged up immediately. However, the Pooprints kits must be dried for 30-40 minutes making the possibility of mixing up unlabeled swabs drying on a table much more likely.
The Pooprints process is not necessarily bad, but id does require very careful attention and strict management when swabbing more than one dog at a time.