David here, Shopify Guru.
If you were looking for a reputable partner in this field, you could check in with some of our Marketing Experts here. These would be experts in both fields of marketing and Shopify, so the tie in there would be great!
If you were looking towards someone in just the fields of Adwords, this website, Upwork, seems to have partners working directly in Adwords, definitely worth taking a look at also!
They wouldn't be directly with Shopify in mind as they are third party, though something to consider also!
Have a great one :)
David W | Shopify Guru
I came across your post, and thought I'd give you my contact info if you're still looking for help managing your AdWords account. I'm the Director of Digital Marketing at 42Connect, and that is exactly what I am in charge of. I've managed millions of dollars in PPC advertising, and have been doing this for nearly 10 years.
If you would like to talk more about your goals and how to go about finding help I'd be more than happy to chat with you about that. Feel free to email me at email@example.com if you are still looking!