Will Merch Sell?
While there isn't a magic spell to guarantee sales, this is a big fear when considering offering merch. I have been there and understand. But that is where reader engagement comes in.
Reader Community
If you don't have at least one place where you have really great engagement with a large group of your readers and superfans, making consistent merch sales may be more difficult. But if you do have that place, whether it is an email list, Facebook page, Facebook group, or even Instagram, then just ask your readers. Pose the question about how they feel about you offering merch. You can even create a poll to make it even easier for your readers.
When we first launched Quinn Loftis Books merch shop, we started with a collection of prints that I had designed and lettered. I didn't post about them before we opened the shop, I just designed things I hoped the readers would like. The prints sold okay. I sold a few, but not a lot.
But then I started seeing a lot of posts in her Facebook group about offering shirts. So I put together some designs and posted mockups of them in the group to find out which designs they liked the most. The readers loved getting to put in their input and suggestions. I launched the shirts in the shop toward the end of 2019 and sales increased 400%.
Even now, years later, posting questions and polls are the best guide for making decisions when it comes to merch. Figure out the place where you have the most readers and the best engagement, and just ask them.