Hi I'm getting this iphone from my sister. But she said I just need to get it fixed. I just want to make sure tht I don't get scammed by paying overprice service. Need someone to tell me what could possibly be wrong with the iphone.

Here's what happen:
- iphone turned off one night....decided to open. must have pressed sth inside while fixing. ( she didn't tell me what or why she opened it)
- Tried to fix it again....phone turn on music was working but volume button didn't work. Music was playing real loud
- tried to charge it but it wasn't charging....

That's the whole story. Could it be the logic board or is it just some lose wiring and needing new battery?