Sorry, can't suspend disbelief

Well, I'll try to explain from my interpretation:

1. Yes the black man was a little irritated with Patty because he thought he might be getting a runaround. Despite what people may believe, racism is alive and well in the US. I know. I'm a black woman and I have definitely been discriminated against because of my race. It's hard to prove in most cases because all people have to do is give a fairly reasonable explanation of the "real" reason you didn't get that job or that apartment, etc. and it looks like we're just playing that ever elusive "race card." But believe me, we're intelligent enough after a few incidents like that to know when race is playing a role. The Asian couple was nice, polite and filled out a credit application no problem. There was no reason to have a problem with them. Drake immediately considered the black man a "minority scam artist." But as soon as a white man came in flashing hundred dollar bills around, he conveniently allowed himself to be pressured into not filling out the credit application.

2. The producers of the movie probably used some artistic license with the actual laws and also hoped viewers would have some suspension of belief in order to make the plot work. If you do that, then you know that every time Drake flies off the handle he's just made things easier for Michael Keaton's bad guy to screw them out of their property.

3. I'm not sure if you're saying that Drake shouldn't be that impressed with $2900 dollars when he has a piece of property worth almost a million dollars. But keep in mind, he and Patty have spent all of their savings to buy and restore the property. Without renting the two apartments, they're broke and unable to make the mortgage and other living expenses. They need that money. I'm broke within two days of my payday. If I depend on a renter to make my expenses, then I'm drooling at the sight of almost three thousand in cash. In fact when he showed that money I was already thinking like a mugger, thinking to myself, 'I'd like to beat him out of that money' lol

4. True on this one. I guess it's another one of those suspension of belief deals. You figure once Carter has changed the locks then you think he's successfully blocked Patty and Drake from the place and they need that elusive eviction in order to get him out and get in there themselves.

5. Greg was in on the scam with Carter. He was just looking to get his share of the money. Other than that we don't know who he was or where he came from and once he and Carter got into that fight, he took off and we never hear from him again :) A "convenient" way to get him out of the picture for the rest of the movie.

6. The movie never explains what exactly Carter did to get cut off from his family and ousted from the family money. We assume based on Patty's phone conversation with the trust handler dude, or whatever you would call him, lol, that Carter was always into shady money making scams or other unlawful activities and they just got tired of bailing him out of trouble and he gets cut off entirely to fend for himself. As for getting beat up, he knows he's going to have to take some crap in order to pull off his real estate scams. In fact, getting himself assaulted by people apparently helps in his case to get landlords so deep in legal trouble that they end up having to hand over money and property to him. Hence, later in the movie when Patty is talking to Beverly D'Angelo's character and Beverly tells her that the landlord of the building where she's living sent over guys to rough up Carter. "And now look who's here and look who's not," she tells Patty.

7. Who really knows the significance of the dismantled Porsche. Maybe it was Carter's plan to further stain Patty and Drake's reputation to have this stolen vehicle in their garage in pieces. He had leased the vehicle and then made one payment on it and took off. He simply leased another after that, a Cadillac as Patty finds out during the sequence when she's trying to track down Carter.

8. Well, I won't claim to know how the laws work everywhere, but I'm assuming, Drake was arrested for assault. Patty or his friend, the black guy maybe paid some sort of bond to get him out of jail, after that he has a restraining order against him and can't go back to the house, which is why he was staying with his friend. He likely has some sort of court date related to the assault, but it just wasn't mentioned in the movie. I don't think he "got off" so much as he was simply awaiting some sort of court date where he would find out if he paid some fine or what. Again I don't know how the law really works around stuff like that, but that's my guess.

9. Well, Patty and Drake are certainly up to their as**es in debt at that point. Both of them are working. So they have some money coming in with which to try to pay their expenses. But it isn't enough to cover everything because we know that they end up way behind on the mortgage obviously since the rental units aren't being used. During dinner with their friend, they talk about how the bank is threatening to foreclose on them because they haven't paid the mortgage, or they're behind on some of the payments. So the money, what little of it there is, comes from their jobs.

I thought the behavior of the black applicant/police detective was realistic. For the initial scene, any race of guy (who knows his credit score is going to be low) would have acted in a similar nervous fashion; though only a black guy would later on attempt to lord it over Melanie Griffith, who actually never got his application (mostly due to the selfish clambering horde behavior of the East Asians and their dumb-as-rocks, possibly Italian mover); though again if I were him, I probably wouldn't buy her technically accurate denial either. Actually the only thing to make all of it even more fabulously realistic would be Michael Keaton's disgraced WASP heir figuring out how to exploit this liberal bourgeois racism angle for mucho publicity & profit.

In real life people do rub in their grievances and Schadenfreude against people perceived to be more snobby, so I didn't mind his "gotcha" moment that much, especially considering that the Bay Area's black middle class was destroyed by political strategies and forces much larger than Matthew Modine or Melanie Griffith.

Your other points are irrelevant because 2) most deadbeats aren't as well-read on exercising their tenancy rights as Michael Keaton was;
3) Modine was obviously unfit as a businessman or property manager, by both temperament & intellect;
4) see #3;
5) the "sculptor" guy was called in as muscle, and obviously due to them alternating shifts if either was going to sleep/leave the apt;
6) getting beat up in the beginning was the strategy for the civil claim;
7) because he felt like it? It was a known stolen car at that point, what keeps him from other wheels?
8) duh, the D.A. didn't pursue it because the victim didn't press charges (so he could try the restraining order gambit, natch) and by that time Keaton was about to be evicted on default -- they even showed, rather clumsily, the two lawyers discussing this at the courthouse
9) both owners were depicted as employed and drawing a regular check apart from the dubious financials of the house/apartment/Airbnb project. In the case of Griffith she might have been raking in a chunk of change from gullible S.F. housewives on the horsey riding lessons for their little brats