Cash purchase limitation under gst

In my view there is no restriction in gst law towards cash transaction.you can purchase in cash.in income tax law if you make an payment more than 10000 for any expenditure in cash it will be disallowed.what is unauthorised dealer? you are tring to say unregistered dealer.If you purchase more than 5000 from unregistered dealer you have to pay gst under RCM Basis.but this RCM provisions is suspended upto 30.06.2018.