Look at Squarespace TOS:
10.2. eCommerce Restrictions. You may not offer or sell any products or services which, in our sole discretion,: (a) we consider hazardous, counterfeit, stolen, fraudulent, abusive or adverse to our interests or reputation; (b) are prohibited for sale, distribution or use; or (c) otherwise fail to comply with any applicable laws or regulations, including without limitation with respect to intellectual property, trade secrets, privacy or publicity rights, consumer protection, product safety or trade regulations or export controls, regulations or sanctions.
So Squarespace considers airguns hazardous you'll be in the same boat,