Most losses on a job are created not on site but while the estimate is being written. Ten recurring mistakes.
No validity date, so the price lives forever. No exclusions section, so everything unwritten is assumed included. No profit line at all, leaving overheads to cover only fuel and management time. Percentages taken from the wrong base — both should come off direct costs. Round sums with no quantities behind them. An unclear VAT position. Quantities bent to fit a price already quoted instead of measured first. One unit of measure for everything. No contingency on renovation work. And an estimate with no company details or signature, which for a bank or an insurer is just a printout.
A simple test before sending: read it as a stranger and ask whether every figure can be checked, whether the exclusions are clear, and until when the price holds.
See the estimate template and templates.