Every trade knows the job that looked simple from the doorway. Lift a floorboard and the joist’s gone. Chase a wall and there’s a cable nobody knew about. Strip the render and half the substrate comes with it. The work was always going to be there — the problem is you’d already given a firm price that assumed it wasn’t.

The instinct is to either guess high and lose the job, or guess low and eat the difference. Neither is necessary. There’s a middle path: price everything you can see properly, and handle what you can’t with a structure the customer understands and agrees to before you start.

Never firm-quote what you haven’t seen

A quote is a fixed price you’re bound to once it’s accepted. That’s fine when you’ve surveyed the work and you know what’s behind, under and inside it. It’s a bad idea the moment your price depends on an assumption you haven’t tested.

The tell is simple. Ask yourself: if I’m wrong about this, who pays? If the answer is “me”, and you haven’t actually checked, that’s an unknown that needs handling — not a number you should be pulling out of the air.

Common ones worth flagging:

What’s under the floor covering, or behind the plaster, tiles or render
The condition of existing pipework, wiring, joists or substrate
Whether existing work is to standard and can be built on or connected to
Ground conditions, drainage runs, buried services
Access — parking, stairs, doorways, whether you can get plant or a skip in
Whether the customer’s finish choices land in the bracket you assumed

If you’re unclear on the difference between a binding quote and a good-faith estimate, that distinction is worth nailing down — it’s the foundation for everything below.

The four tools for pricing an unknown

You don’t need one answer, you need the right tool for each unknown. Most jobs use more than one.

1. A price range

Best when the whole job could go one of two ways and you genuinely can’t say which yet. Give a realistic low and high, and — this is the bit most people skip — say what decides where it lands.

“Between £X and £Y. The low end is if the existing boards are sound and we’re just lifting and relaying. The high end is if they’ve gone and need replacing — I’ll know within an hour of starting and I’ll show you before we go further.”

A range without an explanation reads as vagueness. A range with a stated trigger reads as expertise.

2. A provisional sum

Borrowed from bigger construction jobs, and genuinely useful on domestic work. A provisional sum is a placeholder figure for a specific item you can’t yet price, sitting inside an otherwise firm quote. It’s clearly labelled as provisional, and it’s adjusted — up or down — against the actual cost when the work is known.

It’s the right tool when one element is uncertain but the rest isn’t:

Item	Price	Basis
Strip out and dispose	£X	Fixed
First fix	£X	Fixed
Joist repairs	£X	Provisional sum — allows for 2 joists; adjusted on inspection
Second fix and making good	£X	Fixed

The customer sees a real total, knows exactly which line might move, and knows why. Nobody gets a surprise.

3. A contingency allowance

Different from a provisional sum. A contingency isn’t for a known uncertainty — it’s a buffer for the general risk of a job with a lot of opening up. Some trades carry it visibly as a line the customer can see; others build it quietly into the rates. Both are legitimate.

Be honest with yourself about which you’re doing. A hidden contingency you forget to price is just optimism, and optimism is what turns a profitable job into a break-even one. Whatever buffer you use, it should come off the same foundations as the rest of your pricing — your real day rate and overheads, not a vibe.

4. A paid investigation first

Sometimes the honest answer is that the unknown is too big to price around at all. In that case, sell the investigation as its own small piece of work: lift a section, open up a patch, run a camera, do a proper survey — then quote the real job firmly once you know.

Customers accept this far more readily than trades expect, because the alternative you’re offering them is a padded guess. You’re not being difficult; you’re refusing to charge them for risk that might not exist.

Write the caveats so they actually protect you

A caveat only works if it’s specific. “Subject to unforeseen circumstances” protects nobody — it’s too vague to point at when there’s a disagreement. Name the thing.

Useful phrasing to adapt:

“Price assumes existing pipework is sound and reusable. If it isn’t, replacement is chargeable at £X per metre and will be agreed with you before we proceed.”
“Subject to opening up. Once the tiles are off I’ll confirm the substrate condition and, if the price changes, tell you before any further work.”
“Excludes: making good to decoration, asbestos removal, any works required by hidden defects not visible at survey.”
“Allows for a level, sound existing floor. Levelling compound, if needed, is priced separately.”

Two rules make caveats work. First, the exclusion has to be findable — buried in a wall of small print doesn’t count. Second, every caveat needs a process: what happens when it triggers. Discovery, then a price, then written agreement, then work. Never work first.

That process is the heart of a good scope of work, and it’s worth setting up properly — most job disputes are scope disputes, not price disputes.

Say it out loud, not just on paper

Uncertainty in writing looks like hedging. Uncertainty explained in person looks like experience. Walk the customer through it before you send anything:

Name the unknown plainly. “I can’t see what’s under that floor and neither can anyone else.”
Explain the two outcomes. Best case and worst case, in money.
Tell them how they’ll find out. “You’ll know on day one, not on the final invoice.”
Commit to the process. Nothing extra gets done without a price and a yes.

Do that and a range stops feeling like a get-out clause. The tradesperson who says “it might be £X, might be £Y, here’s exactly when we’ll know” sounds far more competent than the one who gives a confident single number and then turns up with bad news and a bigger bill.

Convert to a firm price the moment you can

The unknown stops being an unknown as soon as it’s exposed — so close it out straight away. Don’t let a provisional sum drift to the end of the job and become an argument on the invoice.

When the floor’s up or the wall’s open:

Photograph it. Two minutes now, and the evidence is unarguable later.
Price the actual work against what you allowed.
Send the adjustment in writing — even a short message, with the revised total.
Get a yes before continuing.
Pass on the saving if it’s cheaper. A provisional sum that only ever moves upwards isn’t a provisional sum, it’s a trap — and customers notice.

That last one is worth more than it costs. Handing back money the customer never expected to see is one of the fastest ways to earn a referral.

The takeaway

You’ll never eliminate the unknown from trade work — you can only decide who carries it. Firm-quoting blind means you carry all of it for free. Price the visible work properly, isolate each unknown with a range, a provisional sum, a contingency or a paid investigation, write specific caveats with a clear process, and convert to a firm price the day the thing is exposed. You end up with fewer arguments, fewer jobs done at a loss, and a reputation for being straight with people about what you don’t yet know.

Queezy lets you build clear, itemised quotes on-site as a branded PDF, so provisional items and exclusions are written down properly from day one — join the waiting list to get in early.

How to Price a Job When You Can't See Everything