Telstra were sending people messages a year ago about the 3G shut down, I had to replace my phone and bought from a real store on sale for $200

But buyers still do not get to keep and use anything for a year and then expect they can get a refund

Especially if you did not buy from an authorised seller, which is the only way you should even consider buying a phone on eBay, especially a $700 one

And there is also always the slim chance the staff member was just telling you this so they could sell you a phone from the store