I know exactly what you mean. You're going through listings with generic descriptions that don't even match what the manufacturer calls them. So let's start with the photos. Typically the gallery will start with exterior photos. Instead of swiping right to see more photos of the exterior and then the interior, swipe left if the app/website enables you to and look at the interior shots first.
Before we go on, note that there's a difference between parking assist package and driver's assist package. The parking assist package will parallel park by itself but it won't have adaptive cruise control.
Okay, back to the photos.
1. Look at the center console at the emergency brake button. If there's circle below it (green one), then it has the driver's assist package. If it doesn't, then it doesn't. It could still have the parking assist package though, so...
2. Look at the center console at the bottom where all the controls are near the arm rest. There will either be a parking assist button or there will just be a blank space.
3. Another way to tell is to look at the steering wheel. The left side will have blank areas if it doesn't have the driver's assist package. Driver's assist package will have all steering wheel buttons on the left side occupied.
Exterior photos don't promise you anything, but it'll help.
The wheels. Look at the wheels. If the wheel doesn't have any black in it, it's likely that it's a base model w/o any packages at all. If it has one of two other fancier wheels that have accented black areas, then it may have packages that you want. Again, it's not a dead giveaway one way or the other.
Look at the front. The windshield will have a camera if it has the driver's assist package.
Look at the price. If the price is under 20k, then it most likely doesn't have the driver's assist package you want and certainly won't have the harman kardon sound system upgrade. Either that or it's got extremely high mileage. If it's priced over 32k, then you're looking at 2017 model with the higher capacity battery. 2016's with what you're looking for should fall into the 23k-26k range I'd say. I got mine for 25k with 12,700 miles and it only has the driver's assist package. Don't look at any that have extremely low mileage like 3k miles. Those have been sitting around on the lot and I wouldn't think too highly of the health of the battery.
SUMMARY:
It is rare that a car will have both the driver's assist package AND the parking assist package. Driver's assist package seems to be more common from my search of i3's.
As far as 2016's go, you won't get the best deal. I have a 2016, but only because I wanted the limited Edition with the Deka World interior that was produced only from April - June. If you want the best deal, you want a 2015 with at least one of the packages with mileage under 20k for $20-21k USD.