Great question! Ya, suppliers will have you fill out an application every now and then and that's perfectly fine =). As long as they don't have you pay them a fee for applying or using their services (like AliExpress) then you should be fine. Usually after you fill out an application the supplier will set up a phone call to make sure that both of your interests align if it's not already in the application.
Hope that helps and let us know if you have any other questions, thanks =)
Have a great day!