Can an iphone 4 still work perfectly functional after it dropping and cracking?

I'm buying my friends iphone 4 off him and he drooped it and the top front where the front camera is cracked kinda bad to where thethe actualt camera andcracked hone speaker part is visibleit but he claims its still fully functional and I checked it out and it does truly look just fine and I plan on buying a replacement screen and changing it so its like its new i'm just a little skeptic abut it the phone is only a few months old so I think it Should be totally fine when I replace the screen. What do you think?

It all depends if the sensors are damaged, or if internal components are damaged.
Test it before you buy it, never buy a damaged smart-phone without testing it.
Ask him if you can have it for a day, and take to your local electronics shop. They'll tell you everthing you'll need, and how much it will cost to repair it,( If repairable).

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