Why do two contractors quote very different rates for the same package tier?

The most common reason is mismatched inclusions rather than one contractor being dishonest and the other fair. Ask both parties whether waterproofing, modular kitchen, wardrobes, boundary wall, design fees and GST are included in their rate, since a lower headline figure often means one or more of these has simply been left out. Aligning package tier, area basis and exclusions before comparing two numbers is the single most useful step in avoiding a bad surprise later.