A useful way to looking at this is:
An exception may not be an exemption.
An exemption is an varation of normal precedence, rules or law, allowed by such. An exception is a violation of normal precedence, rules or law, which is not usual or codified.
Should a businessman have established procedures for pricing goods and services, with no allowance for any variation, then, he is making an exception by offering a price outside those usual procedures for pricing. It is an exception, as his rules no not allow for any exemption.
Should a business offer an "exception" it might be an "exemption". Businesses are not much tied to "Rules of English". There may be codified exemptions that are not explained to customers.
I think we will do well to be concerned that we use the words exemption and exception as best we can, and. perhaps not be too concerned how others may use them.