There are a number of reasons being discussed by booksellers all over the Internet. Some of the reasons I have read include:

1) A desire by some to curtail the profiteers and assure that there are some good books left when the sale opens to the general public.

Certainly, this hinders the online bookseller and limits the number of books that he/she is able to check, but I do not think this is the reason.

2) Another hypothesis I have heard is that booksellers rummaging through the books and scanning them leave the unwanted books in disarray, thus making more work for the volunteers to straighten out the mess, but I do not think this is the reason either.

The time it takes to straighten out tables of books after a couple hundred booksellers have finished rummaging around is probably not any longer than straightening out after a few thousand people during the "open to the public" period.

3) There are also some that believe the cashiers do not like ringing up hundreds of books for booksellers,

This does not make any sense because it is a lot easier to make one sale of hundreds of books to one buyer than to ring up two books for hundreds of customers, so I do not think this is the reason.

4) The volunteers and helpers at the book sales are jealous of booksellers coming in and buying up all the good books to make a profit on them.

I do not doubt that there a people working the book sales and attending them that are jealous of dealers coming in and buying up the valuable books, and this probably does play into the decision to ban scanners, but I do not think it is the primary reason either.

I believe the book sale organizers are genuinely concerned about safety and potential litigation. If you have ever been zapped in the eyes by a careless bookseller with a total disregard for where he/she is pointing their scanner, you know exactly what I mean. You will see spots and/or floaters for a good half hour. If exposed to a direct laser of the intensity of my HP 5P (class II) scanner, I do not doubt that you would suffer some permanent eye damage.

I was personally zapped accidentally by someone using their laser scanner and I could not read ISBN's or the screen on my PDA for almost 45 minutes. I believe laser scanners are being banned from book sales because of liability issues; and with our society being so focused on taking someone to court; the book sale organizers do not want to risk being held responsible for the actions of a careless bookseller. As obnoxious as some of the booksellers I have seen can be, I would not put it past some of them to intentionally zap me if for no other reason than to temporarily give them an edge in buying while my eyes recover.