Petit Biscuit & Gourmandise sur Noisy-Le-Grand

I'm a regular customer for pastries and sometimes bread from this bakery, which I really enjoy. The frangipane galette I bought was particularly good. However, I would have appreciated not getting an unpleasant comment about the incorrectly displayed price. It was listed as €4.50 for an individual galette and €3.60 for a slice. I ordered a slice, which was then priced at €4.50, and I pointed out that wasn't the correct price. Fine, I didn't pay the full €4.50. But I don't want to be made to feel guilty. I left without even being said goodbye! Furthermore, apparently paying by card is a problem. I'm used to paying for my pain au chocolat by card... Should I go to another bakery? Should I only go if this saleswoman isn't there?