What site to use for stores for customers?

you simply can't avoid a monthly fee
even if you get woocommerce/opencart, you have to pay for your webhost
you can get free, but they tag on their own name in the domain name (like: shttp://freewebsitesrus.com.del3213)
not professional, esp. if marketing to customers, plus i think you are only allowed one site

plus you have to purchase each domain annually

plus 'free' ecommerce setups usually require a few paid addons to make them function/look professional

they are more work than the 'paid' setups (shopify/lemonstand/etc.), but they are cheaper (not free, cheaper)

We do Ecomm and fulfillment for several companies. We build and run their stores using Big Cartel and love it.
You have the option to have a free standing store with it's own URL, multiple layout templates, and you can choose between a couple different payment processors.
They have plans that range from $0.00 a month to $20.00 a month, depending on what you want to do with it.

For small use, I generally recommend BigCartel as well. As Industryps said, they offer options for free webstores that still have their own URLs. I believe that the free option cuts off with 5 products, and 1 image per product. Most small brands and bands that I know that sell their own merch use BigCartel, so it's worth a look at least.

no custom domains on the free option for big cartel

each store the op sets up with big cartel will start at $10/month for 25 products, min $120/year for each store
(unless they only want 5 products, then it is free, but without their own domain name)

i pay $15/year for 3 stores with their own domain names, and as many products as i want
if i wanted more stores it would be maybe $40/year
but it is a little more effort/time

I’m a website novice so I’ve been looking around and was thinking about the easy drag and drop option on WIX. How is Big Cartel for novices like me.

big cartel is easy (from what i saw on their pages)
any wix site i have visited has been very slow (tons of scripts in the background)

i would trial big cartel for free (5 products) and see how you like it

BigCartel is pretty easy. You can't Drag & Drop but it's pretty close.

You should check the Shopify Partner Program

Are you looking to make your own website? If yes, why not to open an e-commerce website.