I've never been over charged for shipping by happs. About eight or nine seperate orders. Of course, I buy only small-ish items I know will fit in a UPS okay size (and always on sale or parts only easily available from happs).
(They shouldn't have oversize packed that T-molding, though.)
I agree with sirwoogie, too. Used to work part time at an small phone-line/on-line video adapter place. UPS, FedEx and Airbourne would charge $15-$20 to ship one $10 product; most businesses didn't care, and would have let us charge almost anything for shipping. They usually didn't ask shipping costs. Many would accuss us of trying to cheat them for recommending cheaper options!

It was the consumers and some small businesses that worried about the shipping cost, so we'd recomend shipping one product for $1.37 first class or $3.90 USPS priority (different prices for small thing for something that light). But some would order 12 of this an 3 of that and then demand shipping costs immediately. Small Box A is x grams, medium Box B is 3x grams, 10 of this + 2 of that fit in box A, but will 13 this + 3 that fit? If it doesn't, the shipping weight will be the next level, hurry do it in your head. If we quoted the higher, the buyer might not buy; if we quoted the lower and it really cost the higher, we had to absorb the difference.
Since we charged at cost, it was best if we weighed the fully packaged box to give the final shipping cost. And like happs, even when we shipped at cost, some consumers said we over charged for shipping.
The one thing we did, unlike happs, was try to contact the buyer if we thought they won't like the shipping cost.