But I'm not a disability lawyer and welcome anything an actual lawyer might contribute.
Never practiced disability law, but years before law school, did a lot of stuff on the clerical side involving hundreds of appeals hearings, so I'm a trifle out of date as the procedures have changed.
But the general principle of disability is you have to be incapable of "substantial gainful activity," that meaning there is no 40 hour a week job in the local or regional economy that you could sustain. Your inability to do so must be supported by objective medical evidence.
The easiest way to qualify is if you have what is called a "listed impairment," for instance, you have a diagnosis of epilepsy. However, just having it isn't enough. You have to show you have specific measurable effects from it, for instance, with epilepsy, tonic-clonic seizures at least once a month for three consecutive months, even while adhering to treatment (as well as different criteria for lesser kinds of seizures). If you aren't adhering to treatment and that's why you have the symptoms, then you don't qualify.
So you're best off if you have an impairment that's actually listed and can prove you have the specific effects that mean you presumptively qualify. For instance, if you're missing two limbs that is pretty easy to prove. That presumption can be overcome if, for instance, you still continue working, proving that you are in fact capable of it, but with the presumptive ones, you can often just quit and then file.
Plenty of people aren't in this boat, though. They have to prove they have a condition or number of conditions that singly or in combination render them incapable of "substantial gainful activity." For instance, if you have a seizure every week that renders you incapable of working, you are considered unable to work because it is presumed that no employer will tolerate this level of absenteeism.
If you are unable to engage in a combination of sitting, standing, or walking for eight hours at a time consistently, you are presumed to be incapable of SGA.
Generally an appeals hearing (and if you are where Dave is you probably are in that phase of the proceedings) has a vocational expert testifying effectively on behalf of the government who will try to come up with jobs he thinks you can do from the Dictionary of Occupational Titles or other employment sources. These are often ludicrous jobs that don't exist or barely exist, like surveillance system monitor (a security guard who does nothing but watch monitors even though almost all real security guards also have to walk around and do other menial tasks during the night) or pari-mutuel ticket taker (if you Google this the majority of mentions of this mythical job are from the DOT itself). So you have to prove something objective like the inability to sit, stand, or walk eight hours a day, or that there is literally no job you can do.
So the fakers get around this by munching up a storm. I think Dave is actually a munchie too but the swindlers are mainly doing it for money, even though the behavior is very similar. They will endlessly shop around for doctors who will say the right things until they have a thick enough stack of paper with "objective medical evidence" in it to add up to the criteria for disability.
They often have scuzzy lawyers who specialize in this, who have a network of quacks to generate this nonsense whose main medical skill is putting together the proper medical language with the right buzzwords to match up with the legal definition. (My favorite of these frequent flyers was a pair of brothers where one was a lawyer and the other a literal chiropractor.)
People with real disabilities who don't fit one of the clear-cut definitions also have to do this, but not being fakers, don't have to shop around for sketchy practitioners willing to go along with made-up bullshit. It's still difficult for them.
Another issue Dave has is his substance abuse. Substance abuse does not per se disqualify you from disability, but if the SSA believes it's a contributing factor to your disability and you would not be disabled if you weren't on drugs or alcohol, you are disqualified until you clean up and still have symptoms.
Anyway I believe they have reformed some of these things in the couple of decades since I had anything to do with this stuff, but the general principles remain sound.
tl;dr Dave is doctor shopping to manufacture evidence for his claims of disability.
