The Museum of HP Calculators
Calculators (both HP and otherwise), slide rules and many other collectable objects typically sell for far more on eBay than elsewhere often by factors of 5 to 20. (In a recent case the factor was more than 100.) Old calculators have sold used on eBay while national dealers offered new-in-the-box samples for a fraction of the price. This is great for sellers, and if you're looking for a single item, the eBay price may make sense as the cost of convenience. Serious collectors with limited funds are advised to add other sources to their collecting arsenals. Good deals do happen on eBay but have to pick your auctions very carefully.
To keep costs reasonable when using eBay, decide what an item is worth and stick to it even if you lose. Don't let others decide for you. For example, an item recently sold for about 10 times the value most collectors would place on it. The 2nd highest bidder had bid early and to make sure he wasn't outbid, he set his proxy bid to a price he considered "absolutely insane". The highest bidder apparently decided that it must be worth what the other bidder was willing to pay. The 2nd bidder told me "If he had bid $10 less than my max he would have killed me! Fortunately he outbid me so I was rolling on the floor laughing!"
Note too, that heavy eBay buyers can get a reputation for always winning. One person has claimed that he enjoys biding up the prices on certain people that he knows will always beat him.
While eBay and most sellers encourage early bidding, you should know that one of the best methods of winning an auction at a reasonable price is to bid as late as possible. As the earlier example shows, even an "absolutely insane" early bid is likely to be outbid. Many winning bids come in the last minute of the auction.
Don't be lulled into a false sense of security because you're dealing with "registered users". eBay only verifies your email address when you register. Because people can get unlimited numbers of email accounts they can easily dispose of account names with negative feedback. They can also use multiple accounts to bid up the prices on the items they have for sale and to post positive feedback for themselves. One seller was using (at least) nine email accounts to bid up the prices on his auctions.
If you are contacted by a seller after an auction ends (especially if it's a reserve auction in which the reserve has not been met) make sure the person contacting you is the real seller. Because many sellers send no emails after a reserve has not been met, some scammers have realized that it's easy to pose as the seller and collect money for someone else's item.
If you've placed what seems like a high bid and the reserve has not been met you might want to check the sellers past auctions. Ebay only lists auctions back about a month but this can still be enlightening. One seller has listed the same item for over a year. Apparently, the theory goes that you can set a reserve far above a normal auction price and, eventually, someone will pay it and the difference will more than pay for the repeated listing fees.
Some ebay users make a living by buying and immediately reselling the same items on ebay. They patrol ebay regularly and snap up products with low buy-it-now prices, misspellings, poor descriptions etc. and then resell them, often with a minimum price that is many times what they paid. Some of these sellers add value by doing testing or combining parts and options into complete working kits. Other times, the only value is that they got there first. This is not a scam, but it's listed here because it really bothers some people. Note that some people who do this use, different accounts for buying and selling so it's probably more common than you think.
Many of the pictures shown on eBay are links to existing pictures such as those shown on this site. The sellers usually aren't trying to fool anyone - they just don't want to go to the trouble of creating their own image. Be careful about making assumptions on the condition based on the picture. Most pictures on this site have a small "MoHPC" watermark along one of the edges to help you spot them when they are used like this.
Collectible items usually sell for much higher prices when auctioned one-at-a-time so you'll see some dealers selling the same "rare" item over and over again. Generally the top bid goes down as everyone learns that these items aren't so "rare" after all. Some of these dealers will email the bidders an offer of a "second" item that they "found" that they are willing to sell for the top bid price. They realize that the next top bid will be lower and keeping more sales private hides the fact that the item is available in abundant supply.
Some items sold on eBay, are fake or heavily restored. Ask specific questions of the buyer and watch out for vague responses. (One person selling unlabeled fakes has a feedback rating above 70 and uses other accounts to bid up his prices.)
eBay allows only positive feedback between people who have not had a transaction. If you detect that an auction is fraudulent, you can only praise the seller unless you are willing to buy the item.
Many people are afraid to leave negative feedback because this invites "payback feedback" from the other party. Among many eBay dealers, even a "neutral" comment is regarded as an offense and worthy of a "payback". This is why most eBay feedback is extremely positive, and even a single negative may indicate a serious problem.
Sometimes you can learn more about a seller by sending an email and asking a question about the item. For example, the response from one eBay seller with a +62 rating was: "Take a look at my feedback... I dont need your business...so dont flatter yourself." (Unfortunately not all bad dealers are that obvious.)
Everyone who uses eBay has to agree to the eBay user agreement, however, if you complain to eBay that someone has broken the agreement, eBay may explain that they are unable to do anything at all. Your only choice is to use the eBay feedback system but because most offenders respond with "payback feedback", few people bother.
Buyers and sellers are treated differently: If a buyer fails to complete a transaction 4 times, the account is removed. In order for seller to be removed, the buyer has to make a complaint to firstname.lastname@example.org. Safeharbor then looks at the seller's feedback and might do something if the condition appears "chronic". Of course, this is rare since negative and neutral feedback is discouraged. (See above.)