If a seller is not able to do the work asked for by a buyer (eg, either they just don’t have the ability to do it or it is just not possible with the software etc. they have) surely the buyer should not then have the option to refuse the cancellation request. What is the purpose of the buyer having the option to refuse (without changing what they are currently asking for), when the seller can not do the work that is being asked (and has selected the reason as “I cannot do this”).
Surely the option for refusal by the buyer when the seller cannot do the work (and has stated so) should be removed, unless the buyer changes what is required for the order to something the seller can do/something that is possible with the software etc. the seller has.