I just tried putting a book up for sale on Half.com, and it's not showing when I search for that item. Does it take time to get posted, or should it appear right away?

Check back in half an hour. If it still doesn't show, that's weird.

Thanks Brianna! I waited a half an hour, and there it is. Thanks for saving me the anxiety of wondering if it did go up, if it didn't, if I should repost it etc. etc.

Another question: Why do some books have an ISBN 10 number and an ISBN 13 number?

Get it? HALF an hour....

Maybe someone bought it

the isbn-10 is the traditional isbn. the isbn-13 is a relatively new phenomenon (about a year old), introduced partly because of a number shortage and partly because of some global barcode compatibility issue, IIRC. all books published since the start of 2007 should have an isbn-13 as the official isbn, but because libraries and publishing houses are still transitioning, a lot of new books have both printed on them.

No prob.