In one sentence
You don't have to blindly pay a tradesperson's invoice that significantly exceeds the cost estimate or lists flat fees with no basis — check the quote and the invoice side by side, pay the undisputed portion, and deduct the rest with a stated reason.
Exceeded the cost estimate? What Section 650 BGB says
A cost estimate is not a fixed price — some deviation is normal. But if the invoice rises "significantly" above the estimate, the contractor must notify you without delay (Section 650 BGB). If they fail to do so, you may, depending on the circumstances, refuse the extra costs or terminate the contract. As a rough rule of thumb, overruns of around 15 to 20 percent count as significant — the law doesn't set a rigid threshold; it depends on the individual case.
What matters is the distinction from a fixed-price quote: if you agreed a binding flat price, you generally don't have to bear any extra costs at all. A non-binding cost estimate is allowed to shift — but not arbitrarily and not without notice. So first check which type of quote you were given.
Invoice check: these items are worth a second look
Tradesperson invoices regularly contain items that courts repeatedly object to. Go through the invoice line by line:
- Hourly rates and time worked: Does the billed time match the actual time on site? Hours generously rounded up are open to challenge.
- Minute-by-minute billing: Is every quarter-hour started billed in full even though only a few minutes were actually worked? Courts have repeatedly ruled that crude rounding-up without an agreement can be impermissible.
- Call-out costs: A call-out fee is generally permissible, but it must be agreed or customary in the area and reasonable in amount – a call-out fee on top of fully billed travel time usually isn't.
- Material markups: A moderate markup on materials is standard practice; question excessive markups without a supporting receipt.
- Unagreed extra work: You don't have to accept, unchecked, items that were neither commissioned nor flagged to you.
If in doubt, ask for an itemised, auditable invoice – flat sums with no breakdown make any review much harder.
Pay or refuse? The right middle ground
The most common trap: refusing to pay the whole invoice out of frustration. That's rarely wise. If part of the work is undisputed, pay that part — and deduct only the specifically contested items, with a written reason. Pay the disputed remainder under reservation, or not at all for now, until the matter is resolved.
Anyone who refuses to pay the entire invoice, part of which is legitimate, risks default interest, dunning fees, and a dunning procedure – even for the portion that was owed anyway. So keep a clean separation: what is justified, and what isn't?
Upload both documents – quote and invoice
This is exactly where a structured second opinion helps. Upload the invoice and the cost estimate together: the document analysis compares them side by side, flags suspicious items — such as flat fees with no basis, or line items that weren't in the original quote — and shows the deviation as a percentage. With both documents, the result is far more informative than with the invoice alone.
An initial 60-second assessment is available with no account needed; you get 10 free credits when you register. This doesn't replace legal advice in an individual case, but it reliably shows where it's worth pushing back.
Deduct, dispute, or hand it over
Once you know which items you're contesting, the letter assistant drafts a factual deduction letter: the undisputed amount is stated, the disputed items are named, and payment is made under reservation. If the problem isn't the cost but defective workmanship, the first step isn't a deduction but a demand for cure — give the business a reasonable deadline to fix the defect.
If you can't get any further on your own, hand the case over to a pre-qualified law firm with a single click; your documents and the correspondence you've gathered go with it. To see what costs you might face, read our overview of lawyer fees.
