not really, they must have certain amount of sales in order to be qualify for it ... you can demand to see their GST cert if you suspect they are below the sales value ...
companies which are GST registered means these GST registered companies can claim back the GST paid to their suppliers, and collect the GST from their customers.
companies which are not GST registered cannot claim GST refund, and becomes the end consumer. However, this is still a cost of doing business, and their customer still needs to bear the cost eventually.
Yah, and many a time, they just collect the GST without having to pass it on to the authority ...