Obviously, some ladies will take your request differently than others. But, to me, it's no different than some ladies who ask the guys to wash their face and hands before a session. Some even go so far as to have a special antiseptic soap they want you to use, if they are susceptible to allergies, etc.
The issue you may run into though, especially with the quick BnG sessions, is whether any mouthwash is even available if it's an incall. That's a situation where you may want to have one of those travel-size bottles of Scope in your pocket to offer to the lady.
And, maybe if you take a serving of mouthwash
first, and then offer to the lady, she'll be more receptive, rather than a
"my breath is fine but yours isn't" attitude.
And, by the way, I think it's interesting how you worded it "receiving my services". Isn't she the one providing the service? Well, unless you've named your dick Services.