I'm not too sure whether it's a ranking factor or not, there are varying opinions. I would say it's risky.
Additionally, I don't see what there is to be gained by deleting and recreating a profile that could just get another bad review, Also the person that gave you that bad review can come and leave another one!
I would work with some good customers and ask them to do reviews. Far more productive than trying to hide hide mistakes and Google will love good reviews to.
Explain to your client that resources are better spend on creating some new reviews and if you get enough good ones you can outweigh the bad ones to a large degree. Take a look around, you will see there is plenty of excellent brands that get bad reviews from time to time.