FWIW, many years ago I started a little tech company. I was convinced that we had a compelling product, and we had some initial customers - franchises of a large, worldwide organization. It would be easy to springboard to more and more franchises, before even looking elsewhere for customers.
Turns out that I hate sales. Not coincdentally, I'm also not much good at it. We talked to some marketing agencies, but all of them wanted flat fees, and none of them would consider "performance based" payment.
So, yeah. I wish someone like you had existed at the time.
It doesn't work that way unfortunately. The founder(s) have to sell initially because you know your product the best. No external sales person can come and suddenly get all these sales. You may hate sales but if you want to start a business, you are the best salesperson for your product/service.
There is no magic wand to this. You just learn sales by doing. I am a nerd myself but when I started my company, I automatically started selling which is mostly just trying to talk to potential customers and understanding if your product can solve their problems. Only you know that best in early days.
Or hire someone who can sell.
The reason why many sell themselves is because it's cheaper. The founder knowing the product the best is true but trying to be a world class seller is best left to those who can be a world class seller which many founders fail at.
Marketing agencies don’t do sales, so that makes sense. You can get performance marketing agencies to do cost per lead / cost per acquisition goals, but that’s all through search/social/organic/etc and not actually closing or calling leads.