My client is a trust, company, property developer, executor or some other business entity? (in other words, not a private individual). Is ClozeSure available?

Yes, your client is eligible for ClozeSure.

As long as your client is selling your property, unconditionally, with vacant possession and the other ClozeSure requirements are met, for example, a 10% deposit is paid on exchange of contracts and as long as their buyer consists of one or more private individuals.