Have you ever severely over/underestimated shipping costs?

Have you ever severely over/underestimated shipping costs? And if so, how did it all work out?

A few times..

But on the flipside I overestimated sometimes too.

I just eat it, sometimes I'll ship stuff as media mail when it isn't to make up for it.

Shipping bit me this week. Had this item in the garage for several months and for some reason I thought it was around 15 pounds. Turned out it was about 27 pounds. Not a huge difference in shipping cost, but on an item that you're not making a lot of money on, it stings a bit.

i've been off by a few dollars here and there but i have it down pretty good now.

I have it down these days but made a few mistakes in the past. My biggest mistakes were about dimensional weight. When you have something that doesn't weigh much but don't consider it is oversized and UPS or USPS charges you extra due to size. I take the hit generally and call it a learning experience. If I over estimate more than a few bucks I refund the difference. I usually list everything parcel select through the post office and often it works out cheaper to use Priority mail which is insured and quicker so it's rare that I under estimate anymore.