Relationships are hard work. Friendships, dating, marriages... they all have ups, downs, twists, and turns. Yet another type of relationship that requires some extra TLC is the one between clients and their marketing agency.

Sometimes, just finding the right agency is the biggest hurdle. There are plenty of agency fish in the sea, but you need to find the special one that can adapt and thrive in your company's pond.

Here are six tips for cultivating a lasting, meaningful relationship with your marketing agency of choice.

1. Commit for the long-term

A relationship will never be successful without sufficient levels of commitment from both sides. After a thorough vetting and interviewing process, your team should be confident enough in your choice to fully trust your new agency's abilities.

To get to that point, ask the right questions when comparing your agency candidates:

• Request to speak with the agency owner.
• Meet your project manager; it's important to mesh with the person you'll be in contact with day-to-day.
• Ask for introductions to, or for the bios of, the other key team members; vet their experience.
• Be sure the agency has niche experience in your industry—ask for relevant industry associations, key partnerships, other work they've done in your industry, and longevity in the space.
• Get quantifiable results from the agency's current or past clients in your industry.
• Ask for referrals and use them.

Quality agencies typically won't engage on small, limited-time, or one-off projects. They want to sink their teeth into a meaty, long-term engagement. They want to be your partner and share in your success.

Remember that results take time. Agencies want to work with companies that understand that and won't threaten their contract if leads aren't delivered in Week Two.

Depending on your organizational structure and on buy-in from above, it can take years to change internal processes. In some companies, it goes against the norm to have a monogamous relationship with one agency; at times, the system isn't set up for it. Bend the rules when you find "the one."

2. Trust in the process

The transition to "client" can be hard for internal marketers. It's more than a change in title; it's a new mindset that requires your team to shift perspective and responsibilities. Just as it can be shocking to go from "friend" to "boyfriend/girlfriend" to "fiancé" to "husband/wife," becoming "client" takes some getting used to.

If you're having trouble with the transition, lean on your agency. They've done this hundreds of times. You haven't. Trust in their processes and abilities. Remember all the reasons you chose them: They have a great team you like, they are industry experts, and they deliver results.

As you grow into your client role, remember that as the designated decision-maker in your organization you have the final say. Your team put its trust in you to manage the agency relationship and make the important decisions. Be able to make that decision and stick to it. Trust that your agency won't let you go off in the wrong direction.

3. Give your partner all

Be as transparent as possible, and don't hold back. Your relationship is going to be most fruitful when there's trust and openness from both sides.

Start by sharing all of your past marketing materials—the good and the bad. Agencies need to see where you've been and where you are so they can help you move forward.

Share your current messaging, brand guidelines, collateral, likes and dislikes, aspirations, where you've come up short, and where you've succeeded.

Air your dirty laundry. Agencies don't like surprises down the road. If there was a scandal, tension in the C-suite, or swirling rumors, your agency wants to know about it. You can trust agencies to keep your secrets; better yet, they can help you overcome your challenges.

You'll see the best results when you move on from transactional, project-based agency relationships to true partnerships—partnerships that are built on trust, openness, and honesty.