As you probably know, a lot of companies use the term "business development" as a synonyms for "sales", so at my role as a VP business development I had to do some called emails and calls as well.
It is never easy, even if you have the best product in the world and event if you are the best sales person in the world.
You need to show a need, and the need must stay in the customers head even after the sale so the product will not be shipped back.
If this is not your day job, and you want some extra money, look for a company that is looking for sales people like you, they will usually give you a list of leads based on landing pages or TV commercials followup calls so the call is a bit "warm" and not so cold. There are a few products like that, like health emergency buttons. Just google it or use Indeed to find the relevant position.
Good luck