How much is the agency commission in Poland and what should the brokerage contract say?

Poland has no statutory brokerage commission. The rate, the moment it falls due and what happens if the owner finds a buyer alone are set entirely by the brokerage contract, so the contract - not a market average - is the only reliable answer.

Short answer

There is no statutory commission rate in Poland. The amount is entirely a matter of the brokerage contract.
Because there is no statutory rate, a percentage quoted online is not a benchmark you can rely on. Read the figure off your own contract.
The commission is separate from the statutory costs of the transaction: PCC, the notarial fee and the court fees are paid regardless of whether an agency was involved.
The difference between an open mandate and an exclusive one is contractual, not statutory - the deciding clause is the one that says when the commission falls due.

Why no percentage can be quoted as the rule

Polish law fixes the transfer tax, the maximum notarial fee and the court fees, but it fixes nothing about brokerage commission. Any percentage you read is therefore either a particular agency's price list or somebody's estimate - never a rate you can hold an agency to, and never a rate an agency can hold you to. This is exactly why our purchase-cost calculator defaults the commission field to 0 zł and asks you to type in the amount from your own contract.

Open mandate and exclusive mandate: what actually differs

Both are the same type of contract; what changes is the scope of the agency's right to the fee. Reading the two clauses below tells you more than any label on the front page.

An open mandate: the owner may sign with several agencies and the fee is normally tied to the transaction that a given agency actually brought about.
An exclusive mandate: one agency runs the sale for an agreed period, which is what makes coordinated marketing possible - but the fee clause is drafted more broadly, so read it word for word.
The clause worth reading twice is the one that makes the commission payable even when the owner sells on their own. It is the most frequent source of disputes; ask for a written explanation of how it is meant to work before signing, and have a lawyer look at it if the wording is broad.
A clause on the fee after the mandate ends deserves the same attention: check for how long it runs and to which buyers it applies.

What the commission does not cover

The commission is not a substitute for the statutory costs of the transaction. On a 600,000 zł flat bought on the secondary market with an existing land register, PCC at 2% is 12,000.00 zł, the notarial fee at the half rate of § 6 pkt 19 with 23% VAT is 1,949.55 zł, the deed copies come to about 354.24 zł on a six-copies-of-eight-pages assumption, and the ownership entry is 200.00 zł - 14,503.79 zł, or 2.42% of the price, before any commission at all.

What to put in writing before the first viewing

The fee: the percentage or amount, whether it is net or gross, and the base it is calculated on.
The moment it falls due: which event triggers it - the preliminary contract, the notarial deed or the release of funds.
The term of the contract and how either side terminates it, with the notice period spelled out.
The scope of work covered by the fee: photography, portal listings, viewings, document gathering - and what is charged separately.
Who is registered as the client presented to a given buyer, so that later there is no argument about which agency introduced whom.

How 4property helps the agency

Because the commission lives in the contract, the contract has to be findable. In 4property the brokerage contract is generated from a template, stored with its version and date, and linked to the property card - so the agreed percentage, the mandate type and the expiry date are one click from the listing rather than in an email thread. Viewings and enquiries are logged against the property and the client, which is what documents that a given agency actually introduced a given buyer.