First of all let me say better dont go for second hand phones. we may get so many issues while buying second hand mobiles.
If we dont check it properly.
So I am going to share what all we have to check while buying a second mobile phone.
We have to ask for bill, box and accessories.
Before buying have check about the phone model in internet. Looks the features and specification. While buying just check whether it matches with the phone you are going to buy.
Check it is having original android firmware or custom os. If it is custom os dont buy it. One of my friend bought a second hand phone without checking it correctly. After reaching home when he checked it was custom os and it mallfuncltioning. Now he cant do anything other than calling. The os got crashed.
Check the battery backup because for all second hand there will be issue with battery backup. So go for a service test using service code and Check all functions are working corectly. Like touch, sound, battery , etc
Other main thing you have to get the imei number of that phone by code * #06#. If it is its original imei number ofvl that phone then when you search about that imei number in internet you can get full feature of that phone with its model number.
This are main things you have to check while buying second mobile. If any doubts then you may ask in comment box.