Hi,
It depends on how you configure the Google Analytics plugin and what the client does.
There is basically two ways for HikaShop to notifies GA of a sale:
1. Display some javascript code on a page displayed by the browser of the customer. Obviously, that page can only be after the payment is done, when the customer returns on your website from the payment gateway. There are problems with that: The customer could close the browser before going to that page, or if you didn't configure PayPal to automatically redirect back the customer to your website, he would have to click on a button to go back to the website and thus a lot of sales wouldn't be taken into account. With that method, the current URL is the shop, the previous page is the payment gateway, and the user sending the notification is the customer himself.
2. HikaShop sends a direct call to GA in PHP. This is thus done during the payment notification process when the payment gateway server notifies HikaShop of the payment. With that method the sales are always registered, so in that respect, it is better.
However, the current URL is the payment notification, there is no previous page, and the user sending the notification is your website server.
One mode or another might help with the source of the sale, but it might also give you less accurate analytics on the sales. Testing would be required to see if one mode works better than the other for you.