Chrono24 prove watch is in possession

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Hi all,

I have posted a datejust for sale on Chrono24.
The thing is that my best friend just asked me to be his best man at his upcoming wedding. I thought it would be great to give him the watch as a present! I thus want to remove my listing from chrono24.
Now Chrono24 is stating that my option is to wait until the end of the 3 months sale period, and then prove the watch is still in my possession. It will most likely not be since I'll give it to my buddy.

Could someone please tell me what Chrono24 will be requesting to prove the watch is still in my possession? Will it be a photo of the watch set at a certain time ?

Thanks!