I am a self professed Jewelry whore and I have been this way all my life. A couple of years ago I sold pretty much everything I had on Ebay to buy a specific diamond that I wanted. Now I will preface this by saying that the majority of what I sold were items I purchased through Ebay to begin with. I have never been concerned about fraud by selling on Ebay because I only accept Paypal and I do not ship anything until it has been paid for. Watch you need to keep in mind is that Paypal takes there fee immediately and Ebay invoices you monthly. If you set a reserve price add background colors, fancy font, larger pictures, those extras will cost you even if your item does not sell. PayPal and Ebay will cost you roughly 12% in selling fees total.
Shipping Priority is usually the cheapest way and will run you about 5.70 for a small flat rate box. This gives you free tracking and I believe 50.00 in insurance. If the buyer wants additional insurance only purchase insurance for the amount you sell the item for. Appraisals mean nothing on a claim. Postage is cheaper if purchased online through Ebay and will cost you less then at the post office. Another bonus is the cost of the postage is deducted from your Paypal account.
Make sure you set up your Ebay account to only sell in the US if you choose to sell internationally out of the country you have to fill out customs forms. I have done this a few times but it is a pain. Also people will surprise you the lower your opening price is, the more bidders you will get. This many times ends in bidding wars and you may get more than you paid for something you never thought would sell. The other side is something that has more value can go for considerably less than what you want.
You can cancel an auction I think up to 2 hours prior to the end and having a lot of watchers is also a good sign. My best suggestion is to go on Ebay and look up comparable items and see what they are listed for. You will also have the option to see what similar pieces sold for. Good luck and feel free to pm me any more questions you may have.