Yeah, it’s probably not worth over-interpreting a single sentence found deep within the comprehensive report. The intention there is to describe the general dynamics of expenses—i.e., as volume/revenue increases, commissions inherently rise as well.
Of course, Kamux does not publicly disclose its commission models in detail; someone working in the industry might know, as these are likely quite similar. But in any case, you get some base commission for every car sold, and then there are, as I understand it, both absolute and/or percentage-based commissions tied to both the sales price and the margin. I recall the company saying at some point that absolute euros carry more weight—meaning, just as @Vara-Paavi suspected, cheaper cars have a larger hardware margin in percentage terms. I don’t recall the company commenting on these in more detail than this.
Salespeople certainly prefer selling more expensive (which are also usually newer) cars anyway, because it’s more likely that they can sell add-on services with them. And there are, of course, separate commissions for the sale of those add-on services.