1. Specification precision — the biggest mover
Quotes built from "standard specification" placeholders shift dramatically later. The same brief at different spec precision varies by ±30%. The honest path is to bid only after the detailed-design set (100+ sheets) is complete.
2. Scope inclusions
"JPY 50M total" means different things across contractors:
- Shell only vs. shell + ancillary (exterior works, demolition)
- Soft costs (design supervision) in or out
- VAT inclusive vs. exclusive
Compare "what is included" in a table, not just the bottom line.
3. Contractor experience
Luxury-residence specialists have built-in slack and craft knowledge; volume-builders optimise for repeatability. Asking either to work outside its lane adds 10–20% premium.
4. Risk pricing
Ground, neighbours, labour availability. "Just-in-case" buffers can vary 2× between contractors. Experienced firms price tight; defensive firms pad heavily.
5. Running a clean comparison
Send the same detailed drawings and spec to three contractors with a fixed response template. "Best explanation wins" beats "lowest price wins" every time.
Quote comparison is mainly about discovering what's missing. Half the gap between bids is scope, not price.