The duplicate control against LinkedIn works on Account name. Therefore it can be good to check the account name inside Salesbox before importing a new account. Make sure its the same name.
If do you get a duplicated account, DO THIS:
1. Go to the contact on the account you DO NOT want to keep
2. Click on the contact in the list
3. Click the edit icon on the top left in the contact card
4. Select the account you want to merge/move the contact to
5. Click done
6. Go the the account you want to delete, click delete