Landscaping & decking - registered builder?

Hey guys, I'm currently in process of getting quotes for a substantial amount of work to be done in my backyard, namely, decking, open pergola/structure, screening, turf, etc. I've had a quote from a landscaping/construction company that I'm really keen on, however, upon doing my homework/research with the VBA (Victorian Building Authority), this business is not registered with them, which they tell me they should be if they're doing ANY structural work over $10K. Not being a registered builder, means they won't have the required dometic building insurance they need on jobs over $16K (which this will be). What's the protocol here? Should this raise big red flags? Should I avoid? Really, I'm a bit clueless about all this. Help!