Double shipping issue

[ProfitCode]

Hi! 

We have 2 locations on Shopify. We have products in both locations but we fulfil them from one location only. However, we want that customers would be able to order products from both warehouses.  If it happens that the customer tries to buy products from one warehouse and another one in one order, they would be charged DOUBLE RATE. 

Shopify Please help me with this issue, if you would take a look at forums there are plenty of posts with this issue. Its been happening for 2 years now and it is not fixed! Why can't we have 2 locations or more and only one shipping rate? 

Keep in mind that Shopify recommends Apps, but the apps won't work! Even developers from the apps told me that there is no workaround with this issue. 

This issue motivates me to move away from Shopify...

Thank you all for your help.