The difference is usually due to the condition or edition of the book
plus the urgency to sell.
However there are many books that are listed at high prices where the
seller does not actually have a copy in stock. This means that if an
Amazon Customer buys this particular expensive copy , then the seller
has to search around looking for a copy to buy quickly....then sell it
on to the Amazon Customer at a high profit.
This happens quite a lot on Amazon.co.uk where US sellers are allowed
..to list books at these inflated prices. However if you check their
feedback, then you will quite often discover that it is poor , with
criticism of long dispatch delays + being out-of-stock !...ie they
couldn`t find a copy to resell.
So if you know the true value of a book , then if you spot it at a
bargain price on Amazon, email the seller to confirm its condition ,
then buy it! You can always re-list it back on Amazon at its proper
price and make a profit yourself.
This is common practice .
Have you visited Amazon`s Discussion Board? It can be useful seeing the
true explanations of various Amazon Booksellers methods of selling!
see
http://forums.prospero.com/am-UKsllconnect/start
HTH
Peter