As a product marketer, how do you handle design disagreements on something you're working on with your designer?

Whenever possible I try to have a customer-first, data-driven approach. We've used A/B testing, customer research, or referencing market standards to hash out disagreements in the past. If those aren't an option, but the decision is crucial to the success of the project, I recommend forming a RAPID team/framework to ensure the best option is selected. 

Here are a few things to think about:

1. Consider how you are briefing in the work to get alignment upfront on the ask and the criteria.
2. Related, bring them along on the insights journey to empower them to design in a way that will hit the mark for your target customers. Link them to your customer personas, usage data or research that highlights what they care about, past interaction data or qualitative input from customers and prospects on what they value in design or information architecture.
3. Do you have an opportunity to get feedback directly from users? Is there a way to AB test a creative in a way that would generate useful insights to guide future design decisions? Or do you have a customer advisory board (whether formal, or just an informal handful of customers you could ask for feedback from) that could help you and the designer understand which is the right design path to pursue from the customer’s perspective?
4. Ultimately, try and persuade the designer using customer stories and data. If that isn’t successful, design likely holds the final decision. Use a disagree and commit framework, and ponder what might drive more alignment in the next project you work on together.

I must admit that design disagreements have been rare in my experience. The best way to ensure alignment is to really think of your design partner as a true partner (vs. just a service role), bring them in early and upfront, provide them with context (e.g. maybe even have them be part of planning sessions), and take a collaborative vs. directive approach.

While there may always be one-off disagreements on individual efforts, overall a collaborative approach should lead to a much better working relationship and end result since you’ll now be aligned on goals and desired outcomes.