Product Samples - Inventory and Invoicing issue

Product Samples - Inventory and Invoicing issue

Hello 

I offer product samples to clients and I am not sure how to record it in Zoho Books. If I use an invoice then it is considered a sale, unpaid items and used from the inventory. 

Do I consider the samples as write-off? then it will be bad debt (financial loss) 

Kindly please advise. Much apprexciated