Let's say there is a sign up for merchant and customers. Is it okay if I make the sign up page for the both of them on one page? I added an image here as an example. The sign up is for merchants and the log in is for customers.
Well keep a single form for both of them just differ them on the basis of type like a dropdown with merchant or customer option on sign up. And while signing in, maybe a checkbox maybe which says want to login as a merchant. Depends which one do you want to show as default.
Secondly, apart from this, Don't just give placeholders for input fields because while typing they would disappear. From UX perspective, it is better if you give label on top of the field for better readability.