Ian,
They rely on people being too lazy, which they are, to check prices.
Much like woollies and Coles saying they have the cheapest prices, you need to shop around and know prices.
At the beginning Bunnings were good after they had taken over the Hardwarehouse brand in Queensland.
As time progressed and they sold of the Hardwarehouse stock cheaply, they replaced items with their own suppliers which was a limited range and brands.
If buying one offs, yes, shop around and you will get it cheaper or at least equal. However if you want several items then source it elsewhere and then take advantage of the 10% price difference for the many items you buy.
Works for me. Bought 3 whipper snipers, several barrel bolts, and other things, they don't like it but you can make it work for you.
Tried Masters, they were never in the running. Woollies probably thought they were running another supermarket, they forgot that whilst Coles was behind Bunnings, Wesfarmers (from WA) was behind Coles.