I was motivated to begin my first thread on this site after reading about this subject in a number of other threads. I sell a large volume of cards on eBay, and I would like to share my knowledge with other collectors on the board. I hope that some of you can use this to negotiate deals with sellers in the future. Disclaimer: This is from my personal experience, and there are things that reasonable people could disagree with. Also, this may be a long post, and I apologize in advance for the length.
1. As a Seller, my goal is to sell to a collector. I am a collector. I like other collectors. I like listening to other people talk about what they collect and why they collect it. I hate flippers. Flippers generate most of the chargebacks, bogus returns, bad feedback, etc. If I think that an offer was made by a flipper, there is no chance I would accept an offer below what I believe an item would sell for. If you send a message with your offer, make sure that you don't come across as a flipper when you send it.
2. Courtesy goes a long way. I have received messages from potential buyers that were very professional, and I always consider those offers. Personally, I would never block someone for making an offer on the low end if it came with a professional message like, "I made an offer on your __________ card. I realize it may be lower than what you are trying to get, but I'm over my card budget this month and my wife is gonna kill me if I don't slow down." I would strongly consider selling the card to the guy even though it was a low offer. At the very least, I would send a polite message back.
3. Don't try to convince a seller that their item is worthless. This sounds obvious but I get messages at least once a month telling me, "Your _____ card isn't worth anything. It will never sell. I will give you $5 for it." Those people get blocked. The obvious irony is that they are spending their time trying to buy an item that they purport to be "worthless."
4. If someone has bought from me before, I am more likely to accept a best offer if it is on the low end. I am less likely to accept a low offer from someone I have never done business with before.
5. I will block people who make 3 really low ball offers in succession without actually buying a card in between. If I am asking $100 for a card that regularly sells for $70-80, and I receive an offer for $20 from the same person over and over again. That person will get blocked because they are more than likely a flipper. I hate dealing with flippers.
6. Low Ballers are also potentially "Graders." I hate graders as much or more than I hate flippers. Graders try to get cards for low ball prices to submit to BGS and PSA for big returns on re-sale value. The problem with Graders is that these people often don't have the funds to bankroll all of these card transactions, so they try to intitiate returns on cards that don't "Gem." They would never tell you that is the reason, but they will open a return as "Item Not Described," "Damaged Item," or "Fraudulent Activity."
7. Comps aren't everything. It is perfectly ok to use recent sales as a basis for the offer that you make. However, do not expect a seller to immediately submit to a recent sale price. All auctions are not created equal. There are a lot of sellers on eBay that have no idea how to optimize auctions. If you have a cluster of comps in the same range, that may be indicative of a general price range. However, if a seller has reason to believe that prices will rise in the near future, the seller may want to hang on to the item to be the market maker who nets a comp above recent comps.
I hope that this helps some members of the board to craft future offers with sellers. Be professional in your correspondence, and make sure you come across as a collector rather than a flipper or grader. There are many ways you can convey your status as a collector without giving up leverage in the transaction by seeming overly eager.