Yeah I just ran into that. I bought a set of rancho shocks last night and got bit by the "multiple shipping" BS. I checked 3 different combos (I didn't want to mix brands or "price points" between front and back, nor did I want any of the "economy" brands, most of which I had never heard of) which would have been the only way to pay only 1 shipping fee. my fronts are coming from warehouse A and the rears from warehouse B. There was one Choice of name brand parts I considered that would have been able to get with only 1 shipping fee but we're more expensive per unit but at the end of the day would have been only a couple of bux different overall total than what I chose.
I was able to get the fronts that I did on one of their "closeouts" which basically made up for the 2nd shipping fee vs having gotten the same set of shocks without choosing the "closeout" version, if that makes sense.....
I had a few other small parts I was gonna buy while I was buying from there, but that would be from a "warehouse C" and shipping those parts would have cost more than the parts themselves so I didn't buy those.

One thing I do is to add different combos of compatible parts into the "cart" and see what they would total up to, then dump the cart and try another combo. If it don't work out and I need the parts bad enough there's always buying local. Don't cost anything to look.
On my shocks I need, they were enough cheaper from Rock auto vs local to be well worth buying that way.

I never buy anything has a core attached from there, though.