GST: Who can opt for the composition scheme?

Our client had purchased goods from us before July 1, 2017. They have now returned those goods. Will there be any GST (goods and services tax) applicable on the returned goods? 

GST law contains specific transitional provisions regarding goods sold under the pre-GST regime which are returned by the recipient on or after July 1, 2017. If your client is not registered under the GST law, you should be eligible to claim refund of the taxes/duties paid under the pre-GST regime.

However, the refund is permissible only if the goods were sold prior to six months from July 1, 2017, and are