Genuine reason for sale?

I've always wondered what this means and why it is included in almost every eBay description. 

It's been a while since I lived there, but I don't remember anyone in America caring why a person is selling something. 

What reason would be illegitimate?  Are British people not allowed to sell something because they don't like it?  Because it is getting old and falling apart? 

This seems related to the "polite notice " somehow.




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I bought a couple of second hand cars in the US and always asked why they were selling.  I don't think it's a British thing.