At first you need to understand what exactly is your need.

Like if you want a vendor for your wedding and you want him to create a passage for the entry for the guests so you need to have a references in your mind, Otherwise the vendor is gonna give you all the idea's which you gonna reject because it won't be of your taste or expectations. So always have references in mind.

Second the budget if you have already settled for the limited amount do let the vendor know about it otherwise he's gonna give you all the elements which you don't even need and when you tell him that you won't need that and start cutting things he's gonna loose interest and back out, Even if he does it he'll be not honest with your work which gonna effect your event/function. So always talk about money first and about the thing you want.

When you are choosing the vendors you need to dig a little too about he's background a little too. Like check the Insta Page, Idea's, Google review and recommendations because even if you have done everything right the vendor's intention are not nice sometimes they do things which is unethical. whomever vendor you choose always ask him amount bifurcation for whatever elements he's providing you. Coz sometimes somethings are just overpriced and also ask him about which kind of material he'll be using is it new or the used one, Because if he's giving you the old material then he should not charge you for new one always have everything in written so things will be in your control.

Sometimes you'll also get vendors who haven't done much work in industry but are kind and honest with there work they'll give you good service, good pricing and the idea's that you'll never imagine they can be very experienced or they can be fresher but they'll do their best to make your day the much more memorable.