I have a lot of items I’d like to place on e-bay.But, I’m not sure how to determine shipping ahead of time.After I photograph the item do I box it up and take it to be weighed, or do I just pull an estimate out of what I think it might cost (I’d probably be wrong). Ideally it would be great to charge the exact cost of shipping,but I really hate the idea of having to go to the post office twice. Once to weigh the item, and once to ship it.
What do most people do?
If you know how much the item weighs or even a good estimate you can use the postal rate calculators on www.usps.com or www.ups.com
Another thing to consider…calculate your time and effort to do the posting/shipping work @ minimum wage or whatever you feel is reasonable and add that to the shipping. If you have several auctions closing it will take less time on a per package basis and you can add less per package. If you make a habit out of e-bay selling this will be a nice boost to your income.
Your time has value don’t let anyone tell you this is unexpected or inappropriate.
drachillix is correct in that it is justifiable to charge a “shipping and handling” of whatever you want, although you should disclose it if asked prior to a sale (some sellers post it up front in the auction, some you have to ask). I have seen a couple of outrageous shipping charges. When bidding, I always figure in shipping to see what I’m actually going to end up paying.
How heavy are the items you are selling? You can buy a postage scale at Staples for anywhere from a few bucks, depending on the capacity you need. I think I paid around $20 for a 10-pound scale. The first pound is in ounce increments so I use it in the kitchen, too!
I think most buyers do what I do and figure in shipping to their bid. So I had very good luck with an opposite tack. I posted an item with shipping and handling included in final purchase price. This bit of marketing may have given me a psychological competetive edge against similar items, and it sold for more than my reserve. YMMV.
You have to weigh it already packed in the box first. My shipping is pretty consistent: UPS = $1lb USPS Priority=$2lb (except what fits in a Priority mail envelope which has no weight limit).
Really… I think it’d be a great joke to try to mail a teaspoon or so of, say, something really dense. A black hole wouldn’t fill a teaspoon and would destroy the Earth, but maybe some other type of collapsed star? 
One of my first purchases of Ebay was a postal scale. It weighs up to 5 pounds and I have always been able to give the exact amount of shipping charges for my auctions. It only cost $30 (plus $7.50 shipping and handling) and has been a very good investment.
I usually tell people in my auction that the S&H is a certain fee, which I figured out as the above posts suggest.
For some rather large items (I’ve sold a photo-enlarger and some large electronics) I mentioned in the ad that there would be a range of shipping costs depending on location and to e-mail me for a firm quote based on their zip code.
I also sent a lens to Japan for a collector, charged him a (very small) fee for handling and the actual shipping charges. He wanted it ASAP and he wired me the money.
When I’m bidding, I like to see a quote for S&H. On large items or items with no quote in the auction, I e-mail them and ask before considering bidding.
If you’re crafty you can make a link on your auction to a USPS or UPS rate calculator by zip code & state buyer pays actual shipping.
When we sold off our old TV station equipment (some of it quite heavy) we boxed it all, weighed it on a bathroom scale and rounded up to the nearest full pound. We then went to the UPS rate calculator and got the shipping rate to a residential address in California (we were in NY), and said that “Buyer Pays Actual Shipping, which in the Contiguous US should be around $XX.XX or less”. We then got an actual rate quote to their zip code from the UPS site with our slightly rounded up weight and had them pay that amount.
I just sold some camera lens & the buyer who said that shipping I asked for wasn’t enough so they sent me $6. Then when they got it, they noticed it was another $7, so they sent that to me too. I think thats funny cause in my ad I stated $4 shipping