What does a Dutch estate agent cost and what should the service agreement say?

There is no statutory scale for estate agent fees in the Netherlands. What you pay, and when you pay it, follows entirely from the opdracht tot dienstverlening you sign - which is why that document deserves more attention than the headline percentage.

Short answer

Agent fees are free tariffs. The amount comes from the opdracht tot dienstverlening, not from a rate book.
A buying agent works with a flat fee of roughly 1,500 to 3,500 euro or with a commission of about 0.8% to 1.5% of the purchase price.
The selling agent works for the seller. If you want someone on your side at the viewing, the valuation and the bid, you engage a buying agent yourself.
The buying agent's fee is a purchase cost, so it is not deductible and it cannot be added to the mortgage - it has to come from your own savings.

Free tariffs mean the contract is the only source

Only two items in a Dutch purchase have a fixed price: the transfer tax and the Kadaster registration tariff of 103.50 euro per electronically registered KIK deed. Everything else - the notary, the valuer, the mortgage adviser and both agents - works with free tariffs. That is also why comparing quotes is worth real money and why any percentage quoted without a contract behind it is an indication, not a price.

What to nail down in the opdracht tot dienstverlening

The fee itself: a flat amount or a commission, and if it is a commission, over which amount it is calculated.
Whether the amounts in the quotation are inclusive or exclusive of VAT, so the final invoice holds no surprises.
When the fee falls due: on acceptance of the bid, on signing the purchase agreement, or at the transfer before the notary.
What happens if you buy nothing, or if the purchase falls through on a resolutive condition - and what costs remain payable then.
The duration of the assignment, how each side ends it, and whether there are withdrawal costs when a selling assignment is pulled.
Which services are inside the fee and which are billed on top: photography, floor plans, portal placement, styling, and any advertising budget.

Where the agent's fee sits in the total

On an existing home of 425,000 euro at the 2% rate, with a mortgage and a buying agent, the kosten koper come to about 16,032 euro - 3.8% of the price. Inside that figure the transfer tax is 8,500 euro and the buying agent about 2,500 euro. Cut the agent and the total drops, but so does the support you get on the bid; that is a trade-off, not a saving.

Common misunderstandings

That the selling agent also looks after the buyer. They do not: they act for the seller, and the fee they earn is agreed with the seller.
That the agent's fee can be added to the mortgage. Kosten koper as a whole cannot be financed - they come from your own money.
That everything paid around the purchase is deductible. Only the financing costs are, once: mortgage advice, valuation, and the notary and Kadaster costs of the mortgage deed. The buying agent is a purchase cost and stays at your own expense.
That a percentage found online is a benchmark. With free tariffs it is at best somebody else's price list; ask for a written quotation with the items listed separately.

How 4property helps agents

In 4property the opdracht tot dienstverlening is drawn up from the data already in the file and then tracked to signature, so the fee arrangement is in black and white before the first viewing. The agreed fee, the type of assignment and the end date sit on the property record itself, and every viewing and enquiry is logged against the property and the client - which is what makes the work behind the invoice visible when a client asks what they are paying for.