The calculator takes the weight of the package (and dimensions if UPS,) queries the USPS or UPS site and returns a charge based on their weight tables. I know this because I have programmed shopping carts to do the same thing.
The shipping and handling fee is entered manually in setting up the auction.
The interesting this to see here is HOW they plan to enforce this, what, limit the S & H limited to a percentage of the auction opening or reserve fee amount? And what about weight, how will they enforce that? If someone is limited in the S & H fee somehow, all they have to do is enter 30 lbs for a 2 ounce item, how will they enforce it?
Whatever they do you can rest assured that your interests as a bidder are not the reason for this policy. What they are pissed about is sellers circumnavigating
listing fees. This, in fact, is why you SEE these overbloated shipping fees. Sell something for a dollar, the listing fee is 35 cents. Post something starting at or reserved at $70, it's around $1.80, as I recall.
Secondly, it doesn't take rocket science to figure this out, while I agree this practice is deceptive, the truth is that they are
playing on buyer greed.
Hear me out!

If you dig around for a retail item and the cheapest you can find it is $35, off you go to eBay to see if you can skim off a few bucks. So when you see that item with an opening bid for a buck, HELL YEAH you're in - but then get pissed when the S & H is $30. The bottom line is if they seller doesn't make at least $31 on the deal he may as well not bother selling it at all. This is a simple fact of supply and demand.
BUT . . . he did decieve you into looking at the auction, possibly bidding before you fully looked it over, and is trying to rip of eBay for the listing fees. And THAT is why this practice is WRONG.