Put up a dummy sales page. Show photoshopped images of your product, and have it listed as sold out. Spend a small amount of money on FB ads targeted at who you think your audience is. Calculate traffic to your page and see how many people were at least interested in the product. Try and collect emails to go on a waiting list for when the product is "back in stock"
Don't remember who I learned this from, but alot of people talk about this as a means to validate an idea or potential product
Don't remember who I learned this from, but alot of people talk about this as a means to validate an idea or potential product