I’m guessing that your state has a maximum charge for an acknowledgment and Jurat. That’s what you get paid for your services no matter how far you drive or how long it takes. With that in mind it obviously makes good business sense to also quote a mobile fee to cover all the unknowns. If you drove over to a strangers house and charged $20 for 2 signatures I guarantee every client would offer you a tip. Of course you would turn the tip down because you just needed an excuse to get out of the house till the kids got out of school. And that’s okay because notary service is public service.