The best way i have found to buy Gold off ebay is to do a search for "Scrap Gold" in the search box and lot's of things will come up in the search. Try not to go for anything that has brooches, pendants and stones in them and if your only just starting out then i would suggest to just go for the Necklace and Bracelet items, try and just stick with the 9k chains as they are faster to refine without having to inquart with silver etc... I just break the chain links up into small 1mm pieces and attack with Nitric Acid...
Try and avoid buying brand new gold chains off ebay as you will pay a premium for them and theres a likely chance that they could also be counterfeit. Always ask for the weight of the item, most will give the weight details when dealing in scrap items anyhow.
Once the weight and Karat are identified then do a quick calculation over here: http://www.dendritics.com/scales/metal-calc.asp for the total value that item of jewelery is worth in Gold. Bid on lots of items and don't be tempted to go over the spot price of Gold just because you have to have that ITEM... Just wait another day and something similar will pop up again. I try and buy for 80-90% of spot price and sometimes you will get it cheaper.
Ive bid on approx 20 items the past few days and have only won 1 of those items, however i have made money on that item and if your willing to spend the big bucks you chances are better on winning an item and coming out ahead when buying the scrap gold.
I might even create a thread on some of the items ive purchased and a tutorial on how I process them if anyones interested.
Don't expect an Alchemist type tutorial as i'm still learning how to do all this refining
Good Luck and happy Bidding.