1. RULE ONE: What you see is not always what you get! The SELLER, in order to save time, shows you a scan(s) that only represents what he is offering, and the SELLER keeps re-using that same scan always, week in and week out. So, unless the auction description states that you will receive these exact stamps as shown, be warned that what you get may have the correct number of stamps but may in no way be related to what you see in the picture. CONCLUSION: If you don't want to be BIDDING BLIND, I'd avoid that particular SELLER. (Remember: EBAY is averaging 15,000 to 20,000 stamps auction lots at any one time, so as the saying goes, be patient, as there are many more fish in the sea.)
2. RULE TWO: Don't expect to find unseen treasures!  As is common in human nature, the SELLER will always place his best stamps on show in the scan(s). Therefore, ALWAYS assume that the remaining stamps are junk. BID ACCORDINGLY.
3. RULE THREE: Always seek out SELLERS who show you the majority of the stamps being offered in the auction! If the SELLER really wants to entice you to buy, he will put in the effort to show you as much as possible of what you will be receiving. CONCLUSION: The more scans there are, the better.
4. RULE FOUR: DISREGARD CATALOGUE VALUE when buying MIXTURES!! It is irrelevant! Remember that, according to SCOTTS CATALOGUE VALUE (C.V.), a mixture of 500 stamps has a minimum C.V. of $100.00. Similarly, a mixture of 1000 stamps has a minimum C.V. of $200.00. The minimum catalogue value of any stamp is 20 cents. But if your mixture, as seen in the scan(s), shows you all common stamps only, then you are looking at bidding a maximum of 1.5 cents per stamp on any such mixture. If you are bidding more, then you will probably win but you will also probably be paying too much.
5. RULE FIVE: Always Count, Check and Verify what you receive!! I once purchased 350 stamps and the auction description stated $300+ C.V. The scan showed only stamps that were worth 20 cents or 35 cents, but the SELLER had a rating of 2500+, so I bid and won the auction lot. I found the mixture had only 19 different stamps in all, and that disappointed me, because the SELLER had not stated HEAVY DUPLICATION. Then I went to my SCOTTS CATALOGUE and verified the C.V. only to find that aside from 10 stamps with a C.V. of  75 cents, the remainder of the stamps were all 20c to 35c in C.V. Simple mathematics told me that there should be $1 and $2 Catalogue Value stamps in this MIXTURE. I then contacted the SELLER and advised him that the total C.V. of his auction lot was $95.00 and asked him to send me the remaining $225 C.V. which was missing. He refunded me the full PayPal payment and told me to keep the stamps, apologizing for his mistake. CONCLUSION: He did not make a mistake, what he was doing was hoping that the BUYER was uninformed and having received the mixture, which was at a low cost, that he would not complain or check what he had received. CONCLUSION: I NO LONGER BID IN ANY OF HIS AUCTIONS.
6. RULE SIX: Avoid sellers who charge excessive postage and handling fees!!  EBAY is against this practice, but it continues. You pay $5.00 for postage and handling and the envelope arrives with a 37c stamp affixed. To avoid this, before you bid look at the postage fees. High fees often relate to registered mail costs. Ask yourself, why would you register an envelope for which you paid $7.50 to buy a 500 stamp mixture. CONCLUSION: AVOID THAT SELLER;
7. RULE SEVEN: Be aware that overseas postage Fees are higher than local fees~!! But don't be fooled by high charges. Overseas Airmail costs from Australia to the United States and Worldwide should fall within the  $2.00 to $3.00 range for a Mixture of 500 stamps. Similarly, mixtures of 1000 stamps should be approximately $3.00 to $5.00.  These figures may vary slightly. Registered mail costs more and, if you request it on a letter from Australia, be aware that you won't receive stamps on the envelope as Australia Post only uses PREPAID ENVELOPES for overseas registered mail.
8. RULE EIGHT: Be aware of overseas delays in delivery of envelopes! Airmail to the United States from Australia usually takes anywhere from 10-15 days. The Seller has to prepare the envelope and does not ship same day usually ( unless he states that in his auction description). Be prepared for a further delay of up to 5 days. But don't be shy and contact the seller if you wish to know that the item has been posted. I always go into MY EBAY and click the item to show when the envelope has been posted (some SELLERS do not).
9. RULE NINE: Before bidding, always check the FEEDBACK~!!! Don't just look at the number or the color of the star. Left Click  the number. Then look at the neutral and the negative feedback total. It may take time, as you scroll through, but find the last negative comment. I ignore all the positive feeback. I'm always looking to see how the SELLER handled a complaint. I often then check what comments the SELLER left FOR OTHERS, by clicking that icon. This tells me the type of person that I am dealing with. CONCLUSION: Avoid sellers who are discourteous!
10. RULE TEN: AGAIN, Don't be shy, contact the SELLER to clarify any questions that you might have!! He wants you to bid, so he should answer within a reasonable amount of time. Remember asking questions of the seller, within hours of the auction ending, in almost all cases will not result in a reply. Give yourself at least a few days before the auction ends. And if he does not reply then I'd avoid him in future.
11. RULE ELEVEN: Do your homework before you start bidding~!!! Remember the more you prepare, the more you will be able to avoid unpleasant surprises.
12. RULE TWELVE: How to locate Mixtures~!!! There are numerous CATEGORIES where you will find mixtures. Don't assume that the SELLER will place his mixture in the correct category. Sometimes there are bargains to be had when, say, a NEW ZEALAND mixture of 500 stamps is listed under  U.K. Collections. It, in fact, should be listed under  British Commonwealth Other or  Worldwide Collections . CONCLUSION: Search by using  500, 1000, 5000 and that will bring up all auction lot descriptions which carry those numbers and, depending on what you are looking for, you might find something that is listed in the incorrect category. (As time goes by, I'll be adding further Rules which should help you to enjoy this hobby.)

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AND AS I HAVE ALWAYS STATED, IF YOU HAVE QUESTIONS, IT IS BEST TO CONTACT THE SELLER,

OR MYSELF AND I SHALL SEE IF I CAN HELP YOU.

SO, ALTHOUGH I HAVE A HIGH RATING, HAVING DEALT WITH MANY BIDDERS, FOR ME THIS IS FUN IN A HOBBY THAT I HAVE OVER 45 YEARS EXPERIENCE.

I LOOK FORWARD TO YOUR QUESTIONS...

LEO