It's easy to buy on eBay.  Just sign up, bid and pay.  Chances are you'll get exactly what you paid for.  And the odds are pretty good that unless you follow these suggestions you'll probably regret it.

1.  Know Your Product.  Let's say you're in the market for a Slabovian framish.  What is a good price for one?  Is one made in 1920 worth more than one made in 1946?  Can you tell a real one from a fake?

2.  Search Before You Bid.  Many buyers find an item and immediately start bidding without taking time to see if a similar or better item is offered at another location.  If you find several similar items, you might put some on your watch list to see what they are going for.  You might be surprised how much a small piece of tsavorite will fetch, or how little an antique Charlie Chaplin pencil box sells for.

3.  Look!  Then Look Again.  Any good salesman puts the best face on his product.  Words like "fantastic" are just an opinion at best.  Gold may be a color not the metal, and weasel words like "wood-like", "created", "faux", and "appearing" abound.  Pictures, too, can be deceptive. I once bought a lovely piece of jade, at least the end shown in the photo was.  The other end was an ugly brown.  I got my money back, but stll lost on the deal.  More about that later.

4.  How Big Is It?  One of the most common complaints of buyers is "I thought it was bigger".  There are two reasons for this.  One is they didn't read read the description carefully, which we've already mentioned.  The other is that many sites give dimensions in centimeters which the average American understands about as well as he understands Klingon.  I keep scratch paper and a tape measure by my computer.  When in doubt, I sketch out the size to see if it's what I want.

5.  It's eBay, Not Christmas.  No reasonable person would expect to get a 2 caret diamond for $0.99.  I'll say nothing more about this except to invite you to spend an idle hour viewing the negative ratings given some sellers by people who were disappointed when they recieved a .02 caret stone instead.

6.  How Much Does It Really Cost?  Shipping cost on large items are usually determined by weight, but shipping charges for small items can be quite a shock to the unwary.  "Reasonable" charges from places like Hong Kong can run $15 or more.  So the item you thought you bought for $2.00 winds up costing you $17.00.  And if you don't like it, you can mail it back (at your own expense) and get your $2.00 back.  Most sellers do not refund shipping charges and some even charge a restocking fee.  There is/was one site which sells 2 ct "lab grown diamond simulates" for $0.01 each.  The shipping charge - $30.00.  One site, perhaps unintentionally honest, admits its shipping and handling charges include not just packaging and postage but "packers salary, and our profit". (Italic mine).

7.  Don't Overbid.  Decide what the maximum is that you are willing to pay for an item before you get involved.  I recently watched as 2 people who would not be outbid ran the price of a $25 item up to over $250.  I dropped the seller an email telling him I hoped he'd get more items of that nature but added jokingly that I wasn't going to pay $250 for them.  His answer was that bidders like that made him nervous because he was afraid they'd realize how much they'd overpaid and either not pay or return it later for refund. 

8.  You'll Probably Get Another Chance.  Any good businessman keeps an eye on how well his stock moves.  If it sells well, he'll get more.  And, at least on eBay, if it doesn't sell it will probably be re-listed.  So it's rare that this will be your only shot at this or a similar item.  Keep looking.  It will probably come around again.

9.  Who Are You Dealing With?  eBay gives you a lot of useful information whenever you log on to a site, where the company is located, how long they've been in business, and what percentage of buyers were satisfied.  But don't stop there.  Look at the negatives.  Who wrote them and why?  Some people just can't be satisfied.  Look and see how often the complainer has made what others regard as unreasonable complaints.  Remember that a package containing 5 items that get damaged in the mail may result in 5 separate negatives from the same person.  On the other hand, regardless of what his numbers are, I get very leery of people who have complaints about not replying to emails, dragging their feet on refunds, or shipments that never get received.  A little practice can separate the two groups.

10.  Be Patient.  Orders from overseas can take a long time to arrive, and distance is not always the deciding factor.  For reasons understood only by the post office, I generally receive items from Thailand or Australia much quicker than items from Canada.  Go figure.

Hope this helps.  I'd be interested in your feedback, especially about things I might have overlook.