How as a Seller can I properly calculating the shipping cost of an item

[gchabs]

I am relatively new to mass selling on Ebay, and have been reading about how to properly calculate shipping as a Seller and the problems encountered when you provide inaccurate dimensions and weight of a package when listing an item and when the actual price differs when the Buyer purchases the item/or even provide accurate dimensions and weight and the same thing happens.   This has happened to me a couple of times, but I think it is because while I initially intended to use one size of box, I then used a larger box that was over 12" x 12" x 12".  So I am looking for some affirmation here that I am doing things right.  Are the assumptions below correct?

1. Get the exact box you intend to use to send an item and list those exact dimensions and weight in the listing.  This should result in the buyer being charged the exact amount that it will cost you to mail the item.
2. Select USPS Priority Mail/UPS or FedEx, rather than USPS Parcel Select unless for truly large and heavy items (over 15 1bs and over 15" x 15" x 15"). (I didn't find these dimensions anyplace, it's just something I am assuming is safe - am I correct?)
3. Leave my preferences in my account for Ebay to calculate postage to retail rather than Ebay pricing, which will give me  a bit of a buffer in case there is a small disparity.
4. Is it smarter to use USPS Priority Mail, UPS or FedEx.  I have noticed sometimes UPS is cheaper than the other two.  I just want to make sure that the buyer pays as little as possible and that I don't get stuck with paying more than they have paid.
5. Is there anything else I should do to insure I only end up spending what the buyer paid for shipping and no more?
6. How do I include insurance, or cost of delivery signatures on some of the more expensive items?  Do I simply hide those costs into the price the item is offered? 

FYI, I am selling mostly stuff from my house I have collected over the years.  So, no uniformity in size and weight, item by item. 

Sorry for the long post, and thank you in advance for your assistance.  gchabs 

[nobody*s_perfect]

I know very little about shipping via UPS and FedEx, but a lot about shipping via USPS.

The USPS threshold for "dimensional weight" is 1 cubic foot (1728 cubic inches). Above that size, it's very important to list accurate package dimensions because even a 1-inch difference can have a big impact on postage cost.

Parcel Select is the online equivalent or Retail Ground; both services used to be known as Parcel Post. You can compare costs for those services vs Priority Mail here. Note that you can choose either retail ("in store") or online ("eBay") pricing.

http://www.ebay.com/shp/Calculator

For extra costs like insurance, signature Confirmation, packaging, etc., you can either add that to your asking price or set up your shipping calculator with a handling fee.

[erkosuniverse]

Welcome to E-bay,

One nice method when using usps retail ground is also list FLAT RATE Priority as well 2 options for the buyer

This way a buyer can decide is retail lower cost or should i buy the priority option

Such as if you are shipping from Maine to Texas ( a long way) it is likely priority flat rate will be better choice than usps retail

Remember Flat Rate Priority is a box of its own (small,medium,large)

Priority is just that (shipping rate)

Keep in mind,Now a days many buyers are reluctant to use Fed-Ex or UPS,Due to porch pirates,their items being taken from home delivery's

You can always include all those shipping platforms,this way once again the buyer will pick what they want,when you list you will see the drop down for adding shipping service.

Happy Selling and Many Sales To You!

[gchabs]

Thank you for the info.  

[glgenterprise]

You're usually going to fair better with UPS or Fedex for larger than 1 cubic foot (12" x 12" x 12"). I use Fedex but it is more convenient for me location-wise and the rates are usually pretty comparable.

The thing that is MOST important when creating your listings is being sure you have a box that meets your stated dimensions AND if there is a dimension over 12" be sure you select Large Package. Though it should be a an easy programming step, eBay does not account for dimensional size in their shipping calculator unless you select Large Package, regardless of whether you enter dimensions or not. I've gotten hosed on this a couple of times and lost money on shipping.