RamblingAnn: I don't think anyone specifically answered your question, but yes, if returns to B&M store are allowed, then you do not have to refund the shipping. In other words, you can just return the item and get what you paid for it back.
In fact, this is also true even if you have to mail it back. You may have to pay the shipping to return the item to the retailer (but sometimes not), but I don't think you ever get back-charged shipping for returned items.
Phew, that was kind of confusing.
Bottom line, I do a ton of online ordering, & I have never encountered a situation where I got free shipping to me, but then was somehow back charged for it when I returned something. That just doesn't happen.
Of course this is all in the US. If you are outside the US, I'm not sure what happens, but I think the rules are very different.
ETA: guilty as charged to using girl math. I always add things on to get free shipping. I'm another one who just hates to pay for shipping if it can be avoided!