Buying second hand devices from an unknown source could be little bit tricky.
One of the biggest concerns for smartphone users generally is the battery life. A new iPhone 6 gives normally one and a half day of battery life with normal usage. You must test the battery life of your used iPhone before you decide to buy it.
To check if the battery is in good condition, use all the features of the iPhone simultaneously. Like set the screen brightness to maximum, turn on the WiFi and Bluetooth, start taking pictures and making videos quickly and then make a call of at least 3 minutes. If the device battery goes down very quickly and you find your device is getting hot or your device is switching off at certain percentage (ie 40%) it is most probably because the battery is due to service and replacing.
This is something you should not be afraid when buying from us. Our phones will have passed our industry leading quality assurance programme, which involves testing the battery capacity, number of cycles, charging current and time. If the battery fails in any of those tests we replace battery for a brand new one! You can be guaranteed that the battery in your device is healthy and will not give our problems. We do our best to make sure that product you receive is in 100% working order. These tests are simply not performed when buying from private sellers, many sellers on eBay or small refurbish companies.
Buy SAFE, buy SMART!