First of it's really hard to sell stuff, especially when you are not in front of them actually showing the product off and letting them tush it, feel it. Problem selling stuff is the reason so many companies default each year.
To my experience most smaller channels that succeed in selling merch are the once that really focus on building a community. Where you have a lot of lojal subscribers who watch and comment on every video and where the community aspect have picked up in a way where they start to integrate with each other.
Then let's say you always start your weekly Start Wars talk episode with "Good morning friends, when you lift up your merch cup with coffee and take a big sip in front of the camera. And then you say hey team I have this new channel cup that will be available for sale this month only so make sure to check out the store!". Then during the rest of the show you repeatable take sips of coffee from the cup in front of the camera while talking about Star Wars. To bring even more focus on the merch without overselling you can talk about coffee rather than the cup. "Oh this coffee is so good, just what I needed today!" and "what are your favoirte typ of coffee, let me know in the comments".
There is a other option that can work and that's what I call the business option. Let's say you run a business where you create flys for fly fishing that you sell online through your web store. Then you make a channel about fly fishing where you make videos, guides, tutorials etc all connected to fly fishing and make sure to market that store as the best source to get flys.
Booth way are really hard, if it was easy selling merch through YouTube everyone would be rich. Going to take hard work, a lot of time and dedication. But the more of a community or family you can build around your channel the bigger the chance someone will by one of your products.
