We've purchased 3 Tesla vehicles - and each time, there were reports of quality issues.
For our first S (which was delivered to our front door by UPS, without any Tesla representative present), I developed a thorough walkthrough spreadsheet - and when the S P85 arrived, I methodically went through the checklist stepping through everything in the car to verify there weren't any issues. And other than a couple of minor issues (like needing a detailing after coming off the truck), it was fine.
With our 2nd and 3rd deliveries, the delivery inspection got shorter and shorter - and both our 2017 S 100D and 2018 X 100D were OK when we accepted delivery.
All manufacturers have a small percentage of vehicles with issues prior to delivery - often the dealership/service center will take care of those issues before the owner even comes in for delivery - but even with that, a few issues still get through the quality control process.
With Tesla delivering many vehicles each month, it's not surprising there will be a report of at least a few vehicles with issues. If this was widespread, we would see a lot more reports in the media and on the forums, so it should be reasonable to assume that only a small percentage of owners have issues at delivery.
I'd strongly recommend that you prepare for delivery - and when you see the vehicle the first time, take your time to do a thorough inspection. Walk around the car, inspect the paint and finish. Make sure all of the doors, windows, seats, lights, … are working.
If you see minor issues, notify Tesla and decide if you want them to fix them before delivery, or if you're willing to accept the vehicle and get the issues fixed at the next Service Center visit.
And if you see a major issue, just like with any manufacturer, you should be prepared to refuse delivery - and request they provide you a different vehicle without the problem (such as requiring replacing and repainting entire body parts).
Tesla has a very high customer loyalty rating - which they wouldn't have if customers were frequently having issues at delivery.
Hopefully you won't be unlucky enough to hit a major issue - odds are, you should be fine - and drive away with a fantastic vehicle...