Thumbtack.com review: Pricing: started at $15, when picked the notary was given price of $55. Charged $120.00

I typed mobile notary for my city and state, Thumbtack was the online site, I went to the site. they gave list of notaries, my choice Ms. S. Balakrishnan. next to her information was $15. starting price. I sent the information that I needed 1 signature notarized, price was $55. set up appointment for her to go to client's home, caretaker was there with the paperwork which signature was to be to be notarized. client signed, Ms. S. Balakrishnan notarized his signature and the caretaker handed clients credit card to notary which he was charged $120. which was disclosed after the notary was finished. since I wasn't able to be there, I guess shame on me for not asking price 3 or 4 times. I noticed later that there are several reviews about the way she practices billing price after the job is done?