To reiterate what Hasan said, basically what it boils down to is since Authorize.Net is offered by resellers this means your rates for your merchant account and Authorize.Net will vary. If the sales rep you are speaking to is unable to give you a quote for the merchant account they offer and Authorize.Net they probably are shady or at the very least incompetant.

Definitely look for another provider, and if you can, look for several providers. Since the rates and fees offered to you will vary you'll want to shop around and compare fees. Merchant account rate comparison calculators will help make the math easier to do and merchant account rate comparison worksheets will help you gather the data you need to make a comparison.