There is value in a voice identity for your product, service or business.
Some voice over providers balance the scope of projects they do with their desire to maintain the value of their unique voice qualities. If you want a voice to represent your business as an image voice or brand identity, I suggest reviewing the previous projects a voice over artist has done. Take into consideration the usage and audience for your project.
Some talents will have existing contracts which prohibit the talent from voicing projects of competitors, or for a specific category of product or service. (Known as conflicts, restrictions or limitations.)
If you want a relative level of voice exclusivity, your expense will increase. Productions with restrictions also cost more because the voice over talent is prohibited from voicing (and thus receiving income) from projects in the restricted category.