I agree with Izaki's statement but would recommend you research instead. Your job is to create the experience, not to submit to uneducated guesses.
How? Easiest way is to show comparable examples. eBay, Amazon, and other major retailers almost always follow a particular style, and they have the money to research directly how consumers determine whether the product is worth buying. Use those examples.
For example, one of my first projects was to create a task management app within a much larger scheduling app. So I went and found all of the apps that did task management. Not just the big ones, but the smaller ones too, and even those that were out of business. Then, using that research, I made user flows that they all used and determined what was the critical path they chose, and what the similarities were.
At that point -- and this is critical -- I pointed to our differentiation and offered a choice: to go with what everyone else was doing that didn't match our use case, or to go with my suggested path that does. People who make bad decisions are rarely people with poor judgment. Usually they just lack critical data.
So, for yourself, find and provide that data however you can. Then offer the facts in an easily digestible way. If they still go with what you consider is the wrong path, you've at the very least done your job and determined what is the best course of action. Because really that's your job as a UX designer.