Ask HN: Solo freelancers, how do you outsource parts of a project you can't do?

For instance, I am a pretty decent developer and can solve business problems, but I can't design a website/use photoshop nor write good copy to save my life.

I aim to provide my client a packaged product: hire me to solve X business problem for $Y, and I'll take care of making it happen for you.

But that causes issues when clients want a new version of their website/webapp along with a new design and I can't do it unless they provide me with a design/artwork and copy: it's a crappy experience for them, and for me too because I don't have a direct line of communication to the designer/copywriter.

How would you outsource design or copywriting if you can't do it yourself but sell your client on "I'll make it all happen for you"?

How do you ensure the person you're outsourcing to will deliver and not make you look like an idiot to your client?

How do you find such people when you don't have any you've worked with in the past?

How do you present it to your client? Do you tell them you're outsourcing that part to someone else? Do you tell them to whom?