There are venues outside of ECCIE for providers to give each other a heads up about hagglers... even for an "unverified" BP ho.
FYI: haggling with a sex worker,
especially at the last minute while on the way to an agreed upon date is more than uncouth. It poses a threat to her financial well being, even if minimally. And haggling is often times a precursor to other manifestations of boundary pushing such as coercive behavior. But I have a feeling you knew it was at least a little but shady and inappropriate which might be why you created the conditions where her hand was forced and she would either need to relinquish some of her donation and still see you. Or all of what she would be earning by not seeing you at all.
I've given up a few hundred dollars coming to me to assert my right to to not have to engage with jerks who think they can decide my worth for me and I would do it again. Y'all are playing games if you pretend to not know that haggling (like time wasting/fantasy booking and other devaluing and consumptive actions) does indeed fall on a spectrum of actions that sex workers warn each other about. If the shoe were on the other foot and and a provider tried to upsell and tack on X amount of money to the agreed upon donation while a client was minutes out from her in call, I'm sure there would be a full on roasting and scathing review in coed about how horrible and unprofessional she was...