How do I check on an iPhone previous usage?

hey guys! my dad has bought a ‘new’ phone and has having trouble with his phone, all of the contacts has multiplied by 4 and his location is set in Sydney even though we are in Victoria, me and my dad would love to find out if you could know that his phone has been previously owned (maybe the age of the phone??) the phone is an iPhone 8 and has been bought for a random local phone shop. please lmk!

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