Iphone 5s icloud and passcode

Okay so I bought an Iphone 5s off ebay, it is in the post atm, perfect condition.
I bought off ebay the seller found it last december but there was a passcode so he could not find the owner.So he sold it on ebay. The knowlege of it is limited but I got it for a bargin. I checked the EMIE code and it is NOT blocked.
but there are something i'm not familur with eg… How to get past the passcode
If the is the app "Find my iphone" could alert the buyer? Maybe
anyway i just want to know ways of factory reseting it but its not that easy

You will not be able to factory reset it, only the original owner can do it. Yes they can see where its located anytime its connected to Wi-Fi or cel tower.