recognize a real ipad

Nobody can answer this.

Boxes can be re-sealed. Easily.

Serial numbers can be associated with some other iPad, such as the iPad that might originally have occupied the rock-filled box you’re acquiring, before the rock was swapped in.

And more than a few folks posting here have claimed to acquired decices locked by Activation Lock, and usually with sellers that disappear.

Buying second-hand from somebody that can or will disappear is perilous.

And is a common scam.

If unable to physically examine and verify the iPad is undamaged and functional and unlocked, I’d pass in this deal.

But it’s your money and your decision.

Unless purchased from Apple, or an Apple Authorised Retailer, you have no assurance whatsoever that the device is either new or unused.

There is absolutely no way to know what is inside the box unless it is opened. A genuine and honest private seller will have nothing to lose if selling a new/sealed/unused item that has not been previously activated.

If you have any doubts at all, you should walk away. This risk is yours.

I’ve nothing further to add.

It isn’t particularly difficult to “shrink wrap” a box. Unless purchased from Apple, or an Apple Authorised Retailer, you have no assurance whatsoever that the device is either new or unused.

The IMEI is largely irrelevant and is a printed serial number on the box. If the device is powered-on, set-up - and then the actual serial number is accessed from iPad Settings, you can check the serial number here:

Check Your Service and Support Coverage - Apple Support

To reiterate, purchasing privately provides no assurance that the device has not been previously used - or has a warranty of any kind.

Chiara998 wrote:

how can i check when the guarantee has been activated?

Apple Warranty starts at purchase. You can check the serial number against the Apple coverage database.

Check Your Service and Support Coverage - Apple Support

This presupposes the serial number on the box matches the serial number of the product within.

As for ensuring the device Activation Lock status etc, LotusPilot posted that early in this chain.

Be aware that purchasing a pre-owned iPad is fraught with risk - as many are Activation Locked. An Activation Locked device can only be recovered by the previous owner whose AppleID previously and successfully set-up the iPad.

The All Too Common SAD Reality of Buying … - Apple Community

Here is what Apple suggests when purchasing a used device:

Check for Activation Lock before you buy a device from someone else.

Before you buy an iPhone, iPad, or iPod touch, from someone other than Apple or an authorized Apple reseller, make sure that the device is erased and no longer linked to the previous owner’s account. Follow these steps to check if the device is ready to use: 

1. Turn on and unlock the device. 
2. If the passcode lock screen or the Home screen appears, the device hasn't been erased. Ask the seller to completely erase the device by going to Settings > General > Reset > Erase All Content and Settings. Don't take ownership of any used iPhone, iPad, or iPod touch until it's been erased.
3. Begin the device setup process.
4. If you're asked for the previous owner’s Apple ID and password, the device is still linked to their account. Hand the device back to the seller and ask them to enter their password. If the previous owner isn't present, contact them as soon as possible and ask them to use a browser to remove the device from their account. Don't take ownership of any used iPhone, iPad, or iPod touch until it has been removed from the previous owner’s account.

You will know that a device is ready for you to use when you're asked to "Set up your iPhone," “Set up your iPad," or “Set up your iPod” the first time you turn it on.

Chiara998 wrote:

the device is new yet sealed, so it has not been opened and used. I wanted to know if there was a way to know if it is original

Note that used or not, the one year default warranty, as well as the 60 day eligibility for AppleCare+ began counting down the day it was sold by Apple or an Apple Authorized seller.

l'd actually be particularly cautious about a second-hand phone in the hands of a private individual supposedly in a "sealed box that has never been opened". l mean...really...?