Washington Mutual cannot verify checks

I manage a college textbook store. We've recently received a rash of bad checks that bounced when trying to deposit into our business account. So not only do we loose the amount that the check was written out for, we also receive a fee from our bank for depositing the bad check. I understand that this is how it works with most banks. So recently, we've starting verifying checks that are written out to us. We don't get that many in this day in age of debit and credit cards anyways, so there's not much downtime involved with verifying the check with the bank (at most 3 mins). Most banks give you a toll free number you can use and you just enter in the account number on the check. Well it seems like WASHINGTON MUTUAL seems to be the ONLY bank we've dealt with that CANNOT verify a check for a business. I don't see what's the problem here. It's not like we're asking for the person's mother's maiden name, social security number, or fund availability. Other banks don't seem to have a problem with it. So why does WASHINGTON MUTUAL see it as a privacy issue? Wouldn't you want to deter people from writing checks against a closed account? I feel like WaMu is abetting fraudulent check writing by not offering this service. In this day and age of identity theft it seems it should be a no-brainer to offer this service. Keep up with the times WaMu. I'm just glad I don't have a business account with WaMu.