I have had my Karma for over five years now. At the start of ownership, I often felt that I was completing the production process on the car (getting battery modules replaced, a new diff on the back, making sure the recalls had all been done, getting the front airbags replaced, and on and on). Knock on wood, though, these days my car runs very well. I could complain about the AC going warm when the ICE turns on, but that's something I live with and will not be having fixed because I don't want the dash ripped out.
The thing is, that the tech in SF is right (Pat's Garage?). These cars were the very earliest examples of production from a new company. They were built by a highly respected contract manufacturer in Finland (the original Volvo C70 and Porsche Boxsters were made there too) but still it's clear that each car required special attention as it came off the production line (there's a book about it). You should only buy a Fisker if you know the history and what to expect. Of course, now you are in much better shape because you can always take the car to a Karma Automotive service center and they will do everything for you (at a price).
Buying an eight year old Karma with low mileage does not guarantee a reliable vehicle. These cars need to be driven, otherwise they will definitely complain. Even having a VIN over 1500 won't help you, because so few were made. Mine is #1030
and is great. The fact that your software is only on 510 means that the previous owner didn't keep up on maintenance (the current version is 535, though some would advise against that particular version (see forum)).
You buy a Fisker because you love the car and what it represents in automotive history (at least I did), not just because of its looks and the adoring comments. I fully expect mine to 'brick' one day (probably the batteries will fail or something terminal) and I will have to decide whether to fix it or not. Either way, I probably won't get rid of it. That will be the time for it to be a display item in a collection. But until then, I will continue to service it, drive it and get it fixed when necessary.
The bottom line is that even if mine bricked tomorrow, it has been a reliable car for the past five years. It has not stranded me anywhere (except once for twenty minutes when I had to reboot the car with the big black plug - something you might try, by the way - read the forum). But if you think it should be as reliable as a Volkswagen, you will be disappointed - this forum is testament to the challenges that a small group of people have faced.