iPhone Back Not Sealing Properly

I was just on eBay towards buying a backup 4S. The seller says everything perfect but the back is not sealing up! Since its pawn shop they have no idea on how to fix that! So, they are selling it in throwaway price! Here is the image



Can this be fixed up by simple unscrew the back glass and properly inserting it in which i saw on YouTube? or Any serious issues is lying with it?