What's valuable, but not worth stealing even if you could get away with it?

- I'd go bankrupt 0.00001 seconds into the maintenance cycle
  
  The ECU is unable to communicate with the rear RWR antenna, please contact your local Lockheed Martin dealership for service
- I'm sure China would put in a bid for one, your life wouldn't be worth living after though you would need serious plastic surgery a new identity and even if you moved to China I'm pretty sure you would have a accident eventually.

As a normal person with no underground connections, maybe a significantly sized diamond? I don’t even know where to begin to be able to sell it. And any stolen large diamond will definitely raise alarms if I bring it anywhere legal to sell.
- Find a shady diamond dealer in Morocco, that's how my uncle managed it.
  
  Or just any ol pawn shop on the bad side of town. Those guys never notify the police, even when they're legally obligated to do so. Although, if you go to the wrong pawn shop and they know it's stolen, they might just jack you themselves.

Something valuable you say....hmmm, let me think about it for a sec
- Don't forget to rub it with lemons to make the invisible ink visible
- Hold on a minute! I'm taking my minute back

A famous work of art like the Mona Lisa, maybe? It would be super hard to steal and you might not be able to fence it because it's too hot. Something like that would immediately go viral on the news and everyone on the planet would be looking out for it.
- some people steal art just for the thrill and don't even attempt to sell
- Stolen AGAIN?! (The theft plays a part in the painting's fame.)
- I understand from some podcast that the Mona Lisa is famousbecause it was stolen. Before that it was just another painting.

A gallon of printer ink
- That's not necessarily valuable, exactly. Yes, companies charge a lot for consumer ink jet printer ink, but prices go down dramatically when you're talking about commercial printing. A two liter bottle of high-end dye sublimation ink runs about $200 (might be up since I last bought in 2021), and the dye sublimation ink for the HP printer I operate costs about $700/10L.
  If your printer has replaceable print heads that aren't part of the ink cartridge, and if you can retrofit a bulk ink system, then you quickly find out that ink is pretty inexpensive.

A crude oil supertanker. It would probably break international law to sell it to anyone willing to buy it.
- You'd be surprised at how many nations would be willing to break that international law for some cheap oil.
- I feel like "getting away with it" has that covered, so it would be totally worth it.
  
  I thought the stealing part you got away with but not the selling part