It’s possible the smashing occurred during the delivery? I go very early to venues when setting up cakes and, if the cake has more than 2 tiers I assemble them at the venue. This has worked well so far. How big was your bottom tier and how many dowels did you use? I also always use the 15mm cake drums for cakes to ensure it will support the weight. Did the board you use bend as that may have caused the fondant to crack?