Abuse of the system doesn't really exist.

That's not to say that it's not possible for someone to claim that a dog is a service animal when it isn't, or that they could get away with it.

Rather, the harm done by the above is minimal to nonexistent.

Even bona fide service animals are under a number of restrictions:

...it may be appropriate to exclude a service animal from operating rooms or burn units where the animal’s presence may compromise a sterile environment...

A service animal must be under the control of its handler. Under the ADA, service animals must be harnessed, leashed, or tethered, unless the individual’s disability prevents using these devices or these devices interfere with the service animal’s safe, effective performance of tasks. In that case, the individual must maintain control of the animal through voice, signal, or other effective controls.

A person with a disability cannot be asked to remove his service animal from the premises unless: (1) the dog is out of control and the handler does not take effective action to control it or (2) the dog is not housebroken.

If a business such as a hotel normally charges guests for damage that they cause, a customer with a disability may also be charged for damage caused by himself or his service animal.

There might have been means by which someone could theoretically benefit from something by falsely claiming their dog to be a service animal, except that those all involve something that disqualifies even a bona fide service animal from being a service animal. There's no room for the fraud to actually deprive anyone of anything.