Poor shipping calculation is a real killer for business purchases too, because you;re tying that cost to YOUR cost in products. Nothing ticks me off more than spending an hour looking for the best price on parts, only to have it come out being the WORST price, after they add shipping. I just had a nice one the other day. Bought a bunch of shrink tube... Shipping ops were UPS $9, USPS $6. I picked USPS. They said it was an estimate, and I figured it would be a little more. The receipt comes and it says $37. The stuff comes and I realize the idiots put two tiny strips of tube in a whole long box by itself, when they could have just thrown it in the other box. Then the guy added three pounds of stuffing. I'm not exaggerating... I weighed it.
So I call them up and complain... Their response? Basically... 'Oh well'.