Compare like with like
Two quotations cannot be compared by the total alone. Check the measured scope, finish specifications, joinery internals, service works and exclusions. Record provisional allowances separately from fixed items.
Include the whole project
Design fees, surveys, specialist input, delivery, protection, installation and loose furniture may sit in different packages. Make sure the overall budget accounts for each agreed responsibility.
Plan for decisions and unknowns
Existing buildings can reveal conditions after opening up. Agree how changes are documented and approved. A contingency should reflect the actual uncertainty rather than conceal an incomplete scope.