I have had several customers tell me that they could not complete their order because at checkout, they were told their address was deliverable. I have checked with the local USPS and find that the address is correct. If I place the order for them, I can “continue” and complete the order. Is anyone else having this problem and what can I do? Thanks
Diana,
The only thing I can think of is that you have some type of address verification turned on in Authorize.net. Maybe there is a security setting in there somewhere?
As far as I know, CS-Cart doesn't have any kind of address verification built in, so I'd assume it would be with your payment processor.
Thanks,
Brandon
Agree, there is no actual “Address Verification” built-in to CS-Cart that would prevent “Realtime” shipping rates from being returned.
Just a quick thought, and may be a long shot, however, double check what you have entered under Admin>Settings General>Default Location
Make sure you do not have ANYTHING entered in these fields other than perhaps setting your Default Country = UNITED STATES (Considering your customer base is entirely or mostly US based) 
Um, isn't this related to shipping? Wouldn't we want to know what shipping method and whether they are using real-time shipping or not?
My guess is that they are using USPS real-time and that the format of the address is causing their address validation to fail. UPS also uses address validation on their back-end to determine residential from commercial where possible.