I can see a few reasons why a provider might charge more for it over GFE, etc.

 
First, there are not as many gals who do offer it, and by rules of supply and demand, that would justify higher costs.

 
Second, it can be more physically demanding than conventional escorting, and require skills that take time to hone.

 
Third, it requires an investment in various forms of hardware (for wont of a better term) that can cost quite a bit.

-- Modified on 6/17/2022 8:35:40 AM

There's going to have to be a compromise between hiding the good stuff for paying customers and marketing.  I would think you'd want to at least tease your prospective clients with some fetish images (as least suggestive of the fetish.)
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I just assumed it was standard practice to charge more for BDSM activities.