Ted here from Shopify, thanks for reaching out to us!
Your friends are more than welcome to create a store with Shopify while selling these products as they do not violate our Terms of Service or AUP policy. The only thing they would need to double-check is that their payment gateway allows them to sell these products too. All gateways (such as Paypal) have their own terms and conditions for using their services so your friends will need to contact their chosen payment gateway for more information. For example, it wouldn't be possible to use our Shopify Payments gateway as outlined in our Shopify Payments Terms of Service. You are more than welcome to use a different payment gateway though and a list of alternative providers can be found here if you would like to take a look.
Do you use Shopify yourself? If so, how are you finding Shopify so far? If there is anything else I can help you with, please let me know, I'm happy to help!
Thanks for letting me know!
Have you created a business plan to help you drive traffic to your store? Creating a business plan can help describe a business, its products or services, how it earns (or will earn) money, its leadership and staffing, financing, its operations model and many other details essential to its success. It can also help you clarify your strategy and determine what you’ll need to evaluate the viability of your idea or your growth plans. We have a guide and template here to help create a business plan if you would like to take a look.
As well, have you come across our Shopify Academy before? If not, we do offer some fantastic marketing tutorials which I'd for sure recommend signing up for if you have some time. These courses are free too!
Have you completed your SEO as well too so your store can be found on search engines such as Google as mentioned here? SEO can play a huge part in bringing in sales and potential customers. The key to SEO is understanding what your customers will be looking for and ensuring your site is set up to best manage the products and content they are seeking. There's also a great SEO tutorial available with our Shopify Academy if you would like to sign up.
Let me know how this goes and if there is anything else I can help you with, I'm happy to help!