What do you care about more when you're giving advice on a project; that they do what you want them to, or that they give you the credit for this decision?
People aren't that great at taking advice, particularly on something that they've worked hard on. I'm not just talking about the hard advice that you need to take to avoid failing - but the mundane stuff in particular, the little details that your hired experts are meant to really get. People want to be responsible for every little bit of what they create, it's normal.
But I'm brought in to give advice, that's why I'm here.
Maybe, they may have even told you that. But there are other reasons people hire experts as well. Sometimes it's rubber stamping for a superior or sometimes they just want part of your offer - people often want to work with designers so they can sit around and talk about pictures and feel cool. Most of the time though they really want you to come in and help them get their own thinking straight. Note: This is not your thinking.
The clinch is that your clients getting good outcomes is core to your reputation and your ability to get future business more than anything else. This makes your client doing smart things really important to you - more important than you giving them advice.
As much as I'd like them to say: "Man, you're right, Angus. I was being dumb, and your idea is way better, lucky I asked you" - that doesn't happen very much in the real world.
Alright, how do you do it in the room?
Pro tip: Get your best and most important ideas on the table really early in the meeting. Say it like you're non commital and mix it with some less specific alternatives.
After that you can drop the idea and proceed with the meeting as usual. Working through the various angles to the challenge, understanding the multiple stakeholders, establishing a decision making process - however you usually work. What we tend to find is that they come to the same idea you mentioned casually in the opening. Usually in the exact same words but with the preface "what I think we should do..."
But I like the part where I'm right
We all do. We also need to demonstrate our value consistently. That can seem hard when you're constantly not taking credit for your own ideas - but the outcomes will speak for themselves.
Also, your client feels smarter when he's around you so he will like you more. This means he's not only more likely to recommend you but also to bring you in on more and more projects.
This all seems manipulative
Yeah, a little bit. But even if you don't want to seed ideas early on in conversation the approach is still the same - you need to get your clients there without telling them the answers for them to truly own it. That means they get to be right, its part of what they get for hiring you.