An intermediary paid out of a share of the cost the client pays the provider anyway is the usual structure in the distribution of financial products. It is used at every level, including by large, exchange-listed banks.
When you buy an investment fund through a bank or a brokerage company, part of the fund's annual management fee goes back to whoever brought you into that fund. The practice has names of its own in legislation and in professional documents:
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The only difference from our model is the source. With funds, the intermediary's share comes out of the annual management cost. In trading, it comes out of the cost of the trade. The mechanism is the same, and the consequence for the client is the same: the fund's fee stays identical for all of its investors, even when the manager pays no retrocession to anyone.
In the European Union the practice is allowed, but strictly regulated. The share the intermediary receives must bring the client a real benefit and must be shown separately from the other costs, not blended into them.
There are also services where the intermediary may receive nothing at all from the product's provider. In independent investment advice and in portfolio management, the firm may be paid only by the client, directly, through the fee agreed with them. The logic of the ban is simple: where someone picks products in your place, they may not be paid by whoever makes them. Each member state may extend the ban to other services.
The sound rule is the same everywhere the practice is regulated: whoever receives such a payment says openly that they receive it, and out of what. That is why the page you are reading exists.