Doing market research will allow you to get to know your customers better and what they look for when shopping online. There are also analytics within Shopify that provide insight on conversion rates and returning customer rates, where you can compare from before and after charging for shipping. You won’t know for certain until you introduce local delivery and charge Shopify shipping rates. To understand your customers better and what they value the most, contact your existing customer base via email or social media with some survey questions.