Often businesses (or people) are afraid that they will price themselves out of the market and in doing so discount the value of their goods or services. (it is one of the many reasons that manufactures like to control the minimum price of their products sold). If you are convinced that you are able to compete with other designers then stand up for your own value and let your potential costumers know why your price is what it is. For example, if you are an expert at setting up Wix Stores…say so. Price your services accordingly. After all, why should you, the expert, who can quickly and efficiently create a well working e-commerce function be paid less simply because you can do the work quickly. If anything you should receive (and charge) for the fact that by completing a Store quickly (say 1/2 the time that an inexperienced person would use) you are reducing “lost opportunity” by allowing the store owner to start selling sooner.
Never be afraid to ask for what you believe you are worth. If you loose out on a sale simply because someone else will charge less, you likely don’t want the work anyhow. Remember the old question, "Why is there is never enough money to do it right the first time around, but always enough to do it right the second time around?