Email & SMS Marketing. I got as a freelance media buyer back in 2018 and after a couple of years in Facebook and Google ads, I fully transitioned to email marketing, even though I was offering that on the side as a bonus, but it wasn't serious.
I think what differentiates me is that I'm in the perfect place at the moment, I'm not new and I'm not doing all the work myself so clients get shitty emails, rather I have a team that works for me, but I'm also not too big that I will outsource everything, even the communication with the client, like the big agencies are doing. I'm the only main point of client communication and I also have eyes on everything that is happening with clients' strategy and account.