There's a panel gaps/other mega-thread. While the gaps are going to be subjective (only you can determine if you care about panel gaps). There are some insightful things to at least glance at since they are unique to Tesla and not really things you find in other cars.
1) the B pillar camera may have a plastic film over it. If you don't get this film off when the car is new, it's kind of a pain to remove the sticky gunk later. It's very easy to miss this since the film is such a good fit when new. But on my car, I had the film on the passenger side but not the driver side.
2) the model 3's with a power rear trunk may have a problem along the driver side to accommodate the power-strut. some people have seen this misalignment actually mar the metal.
3) Bring some baby wipes so you can try to clean the interior to get rid of the stains. Anything that you can't get with a baby wipe may be best done by Tesla just in case you end up marring something and they blame you. My car was home-delivered with a bunch of black fingerprints all over the white seats, headliner, steering wheel, etc. For the most part, baby wipes got the stains off. But I figure Tesla should at least clean those before you take delivery of a brand new car at a showroom if you're going in.
4) The black trim along the beltline (lower part) of the side windows could be touching. I didn't notice this until a few weeks of ownership, but the metal was kissing when the front door was opened. Tesla says they'll eventually (it's been a few weeks) send someone out to repair the trim.
Pics from the interwebs: