Can Apple detect jailbreak after restore?

It shouldn't if you restored and wiped the device. Sometimes apps can get leftover but I wouldn't worry about that.

 

There are two arguments on this.

One side says yes they can, but the fact of the matter is they don't care. The other side says they can't because restoring (especially if you used DFU Mode) wipes all traces.

It doesn't really matter because up until about 2014 the general procedure was to restore and then see Apple. I've done this multiple times, others have as well and I've never had a problem. There is a reason that restoring and seeing Apple was the procedure and it wasn't because people liked to do restores for no reason.

Lastly, as of early 2014 or so, a jailbreak has to be the culprit before Apple will deny warranty. The most they can now ask you to do if you hand over a jailbroken iPhone is ask you to restore.

If that is the case, and you are handing over a fully restored device do you think Apple is going to care?

My own experience says no they don't. I turned in a 6+ that was fully jailbroken in September 2015 because of a cracked screen. The genius was aware and restored my device, then disappeared into the back with it.

An hour later another genius handed me a brand new replacement because they couldn't get iOS 9 to boot my old phone (duh, because the Apple genius didn't do a DFU restore and it bootlooped!). So, I got a brand new iPhone for the price of a screen replacement AND THE GENIUS KNEW I WAS JAILBROKEN.

So. Take that as you will.

 

I can't answer that. I've never sent Apple a phone as there are at least three Apple stores where I live.

 

In the US, they legally (Magnuson–Moss Warranty Act) cannot deny you warranty service due to jailbreak, as long as the issue is not caused by the jailbreak. So bad battery, hardware, screen issues, etc... all cannot be blamed on JB, so they cannot deny warranty. Anything that could be blamed on JB would easily be fixed by software restore anyway.

 

No, Apple will not charge your card if you return the old iPhone by the due date.

 

If that concerns you, then erase the iPhone before you send it back.
But, you did say that you already restored the iPhone, so you could easily do a restore again, then simply leave it without any setup, just restored as a new phone.
Apple would restore the iPhone anyway, as part of their "refurbish" routine.
No jailbreak would even exist on the iPhone at that point. Your concern is not justified in any way.

 

You seem to be missing an important point. Jailbreak is just software patches, it does not "break" or do anything to the phone hardware. Once you restore the software, it is not jailbroken anymore.