I understand your thoughts.
I would agree if the product was already being sold for an unreasonable base price. However, I think the most important aspect here is that the total of the base price and advertised shipping price still came out to be significantly lower than what you'd get anywhere else.
If you are able to pull this off, I think it's a good strategy because your customers get a deal and you make money. It's a win-win.
As for buying a swimsuit off eBay, you can absolutely do that, but does it come with the same quality control you'd expect from a legit brand?
There's a lot more value being added from here than just dropshipping a product from overseas. You are establishing a brand, which means you are vetting the product for quality, packaging it nicely and making sure your customer gets a brand new product that lives up to expectations.
If you can pull all of that off while still pricing below retail, I'm all for it.