Only one shipping cost for 3 locations

[shanabenittah]

Hi !

I have 3 locations on my website but would like my client to pay only one shipping rate.

Which mean, if my customer wants one item from one location and an other item from an other location so he would pay only one time the rate and also for pick up if the item is not available on the specific location but available in an other location so the customer can pick it up any where he likes.

Has someone already found a solution to that? Thank you in advance for any help.