If you're bringing them on as a co-founder, then they're a co-founder, equity and all. It's a valuable skill as much as programming and sales are (if you're actually building a business, that is).
The issue you'll find is that most of the places to find them will be full of aforementioned BS-ers, or self-titled growth hackers. Have a small LinkedIn hunt at marketers who work in-house at a semi-large organisation - in a lot of places there's a lot of hunger to do more, but large orgs tie your hands and often see marketing as a "support" function over and above a business driving one.
It might also be easier to find a part timer who doesn't want to give up the above security, but wants to exercise their creative muscles, depending on what stage/size biz you've got and your reqs.
Unfortunately those are the types who are most vocal and up front, who you as technical founder always seem to meet.
I'd kill to meet a marketer whose skills of marketing (and selling) matched mine as an Developer.
How wrong I was! The marketing aspect proved to be just as difficult and brain taxing as the coding. In fact, I found it almost impossible to move ahead until I decided to bring on board a co-founder with a marketing background (after a full year of struggling). It was only then that I realised that marketing and sales is a whole art form not unlike programming. Both disciplines need focus and constant energy to bring about results.