You can't package and ship a parcel for less than $3 so they are losing money on small sales like that. It's clearly a loss-leading effort to compete with other online retailers.

Amazon free shipping has been terrible here. Weeks, at best unless you pay for the express options. And yes Walmart is better. One of my recent online purchases (cell phone screen protector) was estimated at 3 weeks delivery on Amazon. I bought the same item from Walmart.com instead and had it in 2 or 3 days.

Amazon's free shipping routinely delivers items worth a few dollars in about ten to twelve hours for me, and I don't live anywhere near a major city. Are you in some extraordinarily remote location?

Small-ish town (~80K) Midwest USA

Are we guessing? Parma, Ohio?

His point is easily seen if you go to the post office/fecex and try to mail 2 bulbs for $3 and see how far you get.

That's retail rates. Depending on the size of the bulbs, you could likely ship them first class for around $1.5. packaging might be another $0.20 assuming the bulbs are already in stuff boxes.

But still, not much room for profit. And from my experience, a lot of big box sellers will just put it in a huge box and pay a much higher rate than necessary for shipping.

I think the GP is implying that Home Depot might have lost money on the sale because the delivery probably cost them more than they earned from selling the light bulbs.

For Home Depot, assuming it's not a mistake, that's probably an investment in persuading customers to look to them first and not shop around.