Car parking and gst

I am writing to seek your professional advice regarding two potential legal issues concerning my recent flat purchase from builder. I would greatly appreciate your expertise in determining whether pursuing arbitration would be the most advantageous course of action in both cases. Issue 1: Parking discrepancy During the purchase process, the sales representative explicitly assured me that the two car parking spaces I purchased would be covered (not stake). Although the agreement vaguely mentions them as "stake/mechanical/open/covered," this specific assurance regarding covered parking significantly influenced my decision to buy both spaces. Now, upon taking possession, I find that the allocated parking spaces are not covered, in fact, it' stake. I believe the sales representative deliberately withheld this information, potentially impacting my purchasing decision. Issue 2: GST discrepancy I purchased the flat in 2023 and was charged a 12% GST on the agreement value at possession. Upon further research, I discovered that the prevailing market rate for GST on flat purchases is 5%. Additionally, if the builder charges 12% GST, they are legally obligated to "pass-back" the difference to the unit owners. My concerns: I am concerned that the sales representative's misrepresentation regarding the parking spaces constitutes a breach of contract and potentially fraud. I am also concerned that the builder's excessive GST charge and lack of "pass-back" violate fair practices and tax regulations. My questions: Given these circumstances, would arbitration be the most effective way to address both the parking and GST issues? Do I have a strong case for pursuing legal action against the builder? What are the potential costs and timeline involved in arbitration?