Question: Should I return this bass (hairline cracks in neck)?

Are those actually cracks? Can you feel an indentation in the wood? They do not look like cracks to me. They could possibly be tool marks that weren’t sanded away properly? Anyway, that doesn’t look like any type of shipping damage. Also, that boxing and packing job was pretty sweet!

 

Those lines are most likely just cosmetic. I’m not sure what might have caused them to be there.

 

I would take it to a local shop and get it checked to see if it is just cosmetic or more.

 

wood is weird. possibly growth marks. something causing a local change to the tree when when it was maturing. excess lingum, a cut, a bruise, etc... not a structural issue.

that box, that should go back. that's some real folk-art packaging.

 

Wow, I don't think I would have accepted that package.

 

That’s actually better than some of the pack jobs on basses I have bought. I can’t say that I would be overly concerned about those marks unless they were flexing open. If you can’t even feel them, they might just be grain or tool marks.

 

Those are color streaks in the wood, caused by a sudden growth spurt. Maybe especially wet weather just as the sap was rising, or a storm that stressed that section of wood.

 

Your neck is growing hairs, that can be resolved on a monthly basis at the barber shop...

 

The streaks are naturally occurring.

 

I agree, I don’t think they are cracks. Try looking at them with a magnifying glass.

 

Although I agree that those aren’t cracks, That’s definitely not how to ship a guitar .

 

I see the headstock is completely bubble wrapped, was the neck bubbled the same? That box looked terrible but in the end it's your cash, your call.

 

Buying instruments online is the same as buying car parts online.
If you know A LOT about car parts you'll probably do OK. If you don't, go to a parts store.
P.S. Your neck is fine, that's just how wood is.