I think they will have tried to connect with itunes.. if the phone is recognised by itunes they may know the power supply works and that the phone can communicate with the computer. sometimes nothing happens and they will try a restore and this will give an error message. It depends what error message they get as to whether they think they can fix it easily. It isn't a true diagnostic test of the components..it is a rough guide. to fix an iphone after any damage means opening and examining the components.
if you feel confident then search through the answers for water damage iphone and follow the instructions on how to clean and which parts to repair. good luck.
any more details would be helpful..