It costs money for any organization to perform administrative tasks. This is quite common, it should not be a surprise. These rules are spelled out in your HOA documents and any experienced agent should be aware of these fees as well.
Most HOAs also have an inspection that should be performed before the closing and there is also usually a fee for this. The buyers should ask for the inspection - no one wants to purchase a home that has HOA violations, so they should get a report that confirms your property is in good standing w/the HOA and you don't have any violations.
If the inspection does indicate any violations, you are probably required to remedy them before closing - this is usually covered in your purchase contract. You should carefully read that section of your contract and possibly have an attorney review it if there are any aspects that you don't understand.