I second this request! We have been looking around and there seems to be no solution. We called Shopify Support and chatted on their live support, to find out that this is not a capability of Shopify currently.
There seems to be no workarounds that are sufficient to accomplish this. It was recommended to us that we use an app to be able to adjust shipping rates on a per item bases. This will not work, because it is all based on the distance from the Vendor and the Customer. If we raise the shipping price on an item because it ships out of somewhere farther away than we are, what if the customer is actually CLOSER to that vendor than we are. Then, they should have a lower shipping rate instead of a higher one. On the other hand, someone else might order the same item, but they might be further than we are from the vendor, which would raise the rate.
Currently, Shopify has the ability to select a vendor for each product. This is what should happen:
1. Make to possible to edit details for each Vendor and include an address.
2. Have the programmers write a rule that says something like:
IF vendor = Vender 1
Change shipping from address to (Vendor 1's address)
3. When the order is placed with Carrier Calculated Shipping, the shipping is calculated based on the Vendor's shipping address instead of the crudentials in the screenshot.
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Shopify has been great about staying up to date and constantly improving, and there seems to be a lot of users out there hoping for this. I hope to see it soon because it is important!