I have a very good health food store with a knowledgeable owner. If she suggests a certain root or herb, can I use it safely for infertility?

Buyer beware. The grapevine and the internet are filled with remedies, herbs, otc drugs, diets, vitamins, supplements, and tricks to 'make you more fertile.' not one is proven: at best they don't work and at worst, could be dangerous. That said: a healthy diet, limiting caffeine and alcohol, avoid tobacco, moderate exercise, and staying healthy all support natural fertility.
Infertility. There are numerous causes of infertility. One has to consider both male and female factors that may cause the condition. Although I am a physician who practice both traditional and alternative treatments, i would recommend looking for a cause of your infertility before spending money in supplemental treatments.
Herbs. Unless they have been tested for heavy metals, and documentation can be provided, i'd skip it. Why spend money on things that "might" be of benefit, when there are a myriad of effective options. Supplements and herbal remedies purported to be of benefit, are money gambled on a guess. Unless there is peer reviewed evidence, save your money.