I haven't used etsy but I've been buying and selling on ebay for 15 years. I have great rating so ebayers are comfortable buying from me. I just sold a silver pendant worth $12 in scrap, but it sold for $220. That's 1800% markup. I wish gold jewlry sold like that.
The trick is to be honest in the listing. The more information you know the better. The pictures are what sell the item. I always use a scale to accurately show the size in at least two different angles. For sparkly jewelry make a short video and attach the you tube link. Always have a picture with a ring sizer. Don't guess in sizes, let the buyer judge that for themselves.
Posting the weight is tricky. Some buyers will look for the weight and only want to pay scrap value for it. So I'd recommend to use an asjective if you want to describe the weight or simply don't post the weight.
Now if a buyer e-mails asking for the weight then be honest and tell them the weight. More often not these are the serious buyers simply wanting to know more.
I usually sell at 3-5 times the scrap weight ( or ask your jeweler friend what retail would be and shoot for half of that.), and use the option for "best offer". Sometimes you will get the low ballers, but 8 outof 10 the first offer will be at least 2-3 times the scrap weight. Now you can choose to haggle or except the offer well above scrap pricing.
In the end it all depends on hard pressed you are for cash. There is always "that guy" that has to have it. So it will sit for a while, sometimes a year or more, but it sells.
I do not recommend craiglist because of scammers and getting robbed. If you choose this path. Only meet in police station parking lots or at a jewelry stores, or any safe public space.
Best of luck, feel free to ask for anything else.