You're right that effective B&M shipping cost is not always free. The brick 'n mortar cost of shipping is anywhere from a lot ("I'd have to drive into the city just for that and pay exorbitant parking garage fees, and I've got too much to do this afternoon...") to nothing ("I'll be in that store tomorrow anyway, and I won't need it until Thursday...")
In the former case, it's unlikely that the tip would impact my decision; in the latter, it very well might. In either case, it goes in the "con" category and, at the margin, changes some fraction of my Amazon-yes-or-no purchase decisions, always in the direction of no.
In the former case, it's unlikely that the tip would impact my decision; in the latter, it very well might. In either case, it goes in the "con" category and, at the margin, changes some fraction of my Amazon-yes-or-no purchase decisions, always in the direction of no.