How to estimate sales for an ecommerce niche?

I've been looking into a particular niche for a few months now. I have samples from several suppliers and I am ready to start my first production run. At first I was going to sell strictly on Amazon FBA because demand looks good but a lot of my competitors have really well designed websites as well as FBA presence.

Is there any way to measure the demand/sales of ecommerce websites? Take wooden sunglasses for example. I didn't even know this niche existed until recently but on Google/Amazon there are many established brands. Surely there aren't many people strictly looking to buy wooden sunglasses right? How profitable can these niches be once you factor in all of the expenses of actually running a business? My product has around a 30-40% profit margin on Amazon but who knows what that number will be once I start getting a website and social media in the mix. Could drop down to nothing due to the astronomical costs of marketing nowadays.

Another thing that throws me off are the social media numbers of brands. They'll have 100k+ likes on Facebook but get 20 likes a post. Similar on Instagram. They look "big" but their traffic says otherwise. This makes me skeptical that these guys are even making money. What do you guys think?