Then came the megalisters - agencies with software that listed all books in print and a contract with publisher's warehouses/library supply services/factors to arrange delivery of in print books to customers.
Then came the "phantom listers" - agencies with software that spiders through the listings of legitimate on line book dealers looking for titles with few (or no) copies listed in Amazon. They then list them at inflated prices. Some of these have more than one alias on Amazon. I think of them as the Piranhas of the Amazon in the ay that they consume the smaller fish.
If and when they receive an order then then try to purchase a copy from one of the "real" owners of the book.[Some are cheeky enough to request as well a"trade discount" on the dealer's price] Small businesses listing on Amazon and abebooks.com must keep their "fulfillment"rating high, so they can ill afford to refuse to supply such parasites.In fact when I requested once that I NOT be obliged to support what I think of as an unethical selling and pricing model I was told
1] that the buyer was a valued long time customer and that 2] I could approach the agency in question and - at THEIR discretion - request that they stop ordering books from me.
Since AZ and ABE take out some % of the list price for the the books sold on their site (as well as monthly listing fees, closing fees and sometimes a portion of the shipping charge ) they can and do make a much greater profit from the high priced phantom listers than from the legitimate reasonably priced offerings of small book dealers, consequently they are not very interested in aggressively policing the situation.
Now there is "Monsoon" and other software to automatically adjust prices on line. In practice most often works to REDUCE the price below the lowest price already listed - a rush to the bottom where books get listed for mere cents.
One tactic I recommend is to search for books and to see the widest range of options is to use "addall.com" It comes in 2 flavours "New' and "Used"and searches around 30 book listing services You can compare prices (ascending or descending) and also see the kind of dealers who sell the books.
Many listings have boilerplate descriptions "we ship fast" "books may have..." etc. which indicate that no human may have examined the object being listed.Other listings have descriptions of content and condition that clearly demonstrate that it is a"real"book from a "real"dealer. When in doubt look for THAT dealers OWN website to ask questions and get personal service.