The best social media platform to sell your product all depends on the product and your audience. If you have a product directly targeted to young teenagers, such as ages 18 and under, Instagram seems to be the best option, because it is a platform that was created around this popular age. However, if you are looking to sell your product to ages 18 and older mostly, I would suggest Facebook due to the fact that it is more popular towards that age range. Now, either platform is good to sell your product to, however you should look into gaining a bigger audience so that you can have more people view your product. I know both Facebook and Instagram have features where you can pay to have a post advertised to reach a certain number of people, which I think is very helpful in getting your product out there. Good luck!