Yes, filing such a claim can be difficult, but there is precedence. If the claimant is able to provide the needed evidence, they have a stronger chance of having their claim honored.
Typically, lawsuits require a “preponderance of the evidence” of liability. Simply put, this means the amount of evidence and its concreteness shows the complaint detailed in the suit is more likely valid than not. Other phrases often used include “clear and convincing evidence” and “highly probable.” Basically, the plaintiff must demonstrate that there is enough evidence that any reasonable person could have concluded that the patron had a known drinking problem, and serving them would create the risk of danger.
On top of this, the plaintiff must show that the four main provings of negligence have been satisfied: duty of care, a breach in duty, direct causation, and damages.