query

If any business is collecting GST from you, they need to mention GSTIN number in their Invoice and name board. Otherwise, you need not pay GST and can inform Tax authority in your area regarding such illegal collection. Similarly a composition dealer who pays GST based on his turnover also cannot collect tax from customers. GSTIN  mentioned in Invoice and name board is in itself a proof that the dealer is a registered dealer and such dealers are legally bound to pay tax to govt and sumbit return in GST portal every month. Moreover, you can login to www.gst.gov.in and click the search tax payer button and find out genuinity of GSTIN number and also can find out whether he is a composition dealer who cannot collect tax from customers.