It is mostly the turn-off factor.
Nothing kills a boner like having her remove your dick from her mouth and inform you of the additional fee for CIM. I actually had that happen once. I think she expected me to truly find my pants and fish out the extra cash.
Same with anal sex. Sometimes it works perfectly, at least for me. And sometimes it doesn’t, either for me or for her. Once she makes you drop down those extra 80 loonies, you feel obligated, and what is worse, she does too. The last thing any of us should be doing is forcing that particular act. That is how it gets removed from her offering list.
While I prefer to have CIM available, if she says she just does BBBJ, it isn’t that big of a deal to warn her. But if she does CIM for some, why not all? Sex workers talk a lot about respect, boundaries, communication, and repeat customers. But an anal surcharge is the opposite of that. If you see her regularly, isn’t it much better for both parties to see if she us up for anal sex and see how it goes, instead of “pay me $80 more and it will be okay”?
That is why I prefer a higher price, regardless of what services occur, instead of pricing for each activity.