I have a iPhone 6.
Re home button, I would say a 'None Apple button' has been put in, it maybe had a new screen and home button, I have not long fitted a genuine Apple one on mine as I know some of the cheaper ones from ebay are rubbish and do not work well .
Pressing right hand and sound button should reboot it.
Has he checked for new any new updates ?
Could be a 'Faulty App' that's causing it to shut down.
Maybe a loose battery connector
Who reconditioned it, a firm or ?.