If you do give a poor review try to provide a specific example supporting it. I am unfamiliar with Yelp; can you leave an anonymous review?

I am afraid of in-person confrontations so I choose a more arm's length approach. Generally this is always an email to the head office. Going above heads is always more effective that going to the source itself. So visit the company website for this market and take a look at the contact page for an email. If need be, I gather the courage to use a customer service telephone line. The preference still is for an email. If the company is at all worth it's salt they will contact you back.

I recently left a Google review which was not anonymous. It has led to some unpleasantness with a shop owner that is reacting in a very mean and confrontational way. She has managed to track me down on FB and has been rather vindictive and hurtful. I have actually considered getting the police involved.

So my recommendation is that if you do leave a review try to do so in a manner which it can't come back on you.