If ur company is in the imprint/tos listed, u are liable. Not the plumber.
Or let's say you are in the footer as a company listed, the customer calls the website and comes to the plumber. They mess up. The boss of the customer's company orders his secretary (who of course does not know the name of the plumber company, and also does not know that your site is a rankandrent site) to call the plumber company, who may find you on their website.
They may find you on your website and report your name, because the plumbername is not included. In court, you will be blamed.
If that's the case, everything just points to you being the contractor. This is misleading and a massive risk for you. You would also be liable for any defects or damages in this case. It is the impression of an average viewer that counts.
This is how it would look legally for me in my homecountry Austria. Im not sure, where u are from but the best way to be on the safe side is to ask a lawyer. If you are from EU, the laws are certainly not much different from mine.