Hi Johnson,
Since I haven't tried this yet, to help you with your concern I had to do a bit of research to figure out how to formulate an answer for you :)
Luckily, I found this post from almost a year ago with the exact same issue as yours, here's the link -
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Also, I read a forum discussion on the shipping rates when drop shipping from more than one drop shipper on the Webmasterworld.com's forum - many have different ways of dealing with the issue, some have decided to offer flat rate shipping for all products (although risky since actual shipping rates may be higher than your published rate). Others also, talked about a special software that you integrate to your site for shipping. Here's the link to the discussion -
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Hope this helps :)