Don´t know if i´t placebo or not in this specific case. I have had my fair share of this kind of experiences in the last 2 decades and can get and idea if someone is a fraud or not. During the summer I worked with one that was exactly as you said a placebo, it helped a bit until I realized it was just that and she wa sjust taking my money every week. Like classic phrases it doesn´t work because you don´t believe it.
Basically she prepared like a cleaning, kind of what you see in the movies. With candles, salt, etc. She did some prayers in what she said was an ancient language. She did the prayer twice and I heard kind of the same words in the same order.