Shipping
Determining how you will ship is both a personal preference as well as what will benefit the customer as well. Offering more than one shipping option is usually the best way to go as people prefer different carriers.
Charge by Weight or Total Purchase Price
This is another choice that will be based on your needs, what you are selling and what works best in your situation. If you know the total weight of your items, including packaging, then you can charge by weight. However, be careful that you are charging enough shipping as you don't want a miscalculation to eat into your profits! It may take some trial and error and shipping several items to determine what would be the best. You can also go to other people's web sites to get an idea of how and what they charge for shipping. The big shipping carriers provide calculators to help you determine the cost of shipping based on weight, location, size and other factors.
UPS- choose your location and look for the link "Calculate Time & Cost"
FedEx - choose your location and look for the link "Service Finder"
DHL - choose your location, then choose "Ship" from the drop-down menu and then "Get Rates"
All of these shipping companies offer many options, such as pickup of the package from your home or business, online scheduling, online printing of postage and much more. So just compare rates, and see what works for you.
You may also want to take into account things such as delivery confirmation, online tracking for your customer and insurance charges. If you are selling rare or valuable items you may want to add these items. There may be other situations where you would want to have these services available if needed, so make sure you figure that into your research.