Many venues have a preferred vendors list they have put together to help couples narrow down what vendors to use for their wedding day. Ask for it, but also find out if the vendors have to pay for their spot on the list. Many venues require a percentage from their preferred vendors, and as the consumer you should know why a business is on the list. Preferred vendor lists that are merit based are generally better, and you will not have to worry that part of what you are paying for is a kick-back to your venue.
Just because a venue has a paid list does not mean the vendors on it are not any good. The problem is that if they have to pay your venue for the privilege of a referral, that cost gets passed on to you. At the end of the day the people that work in every business you hire, regardless of their passion, are in it to support themselves and their families. It does not make sense to lose money on regular jobs, so to prevent a loss and guarantee profit the price needs to be raised. It is perfectly reasonable for a business to want to absorb a 10% loss incurred from paying their venue a fee by marking up your wedding package by 10%. There isn’t anything wrong with this practice, but it is a reality that should be considered if you are on a budget and planning a wedding.
Working with a venue whose preferred vendor list is merit based doesn't mean you shouldn’t do your due diligence when booking any vendors on their list. You should still ask questions and find out what your coordinator’s experience working with a certain DJ is for example. From a simple conversation you might find out about the DJ’s timeliness, music variety, or pricing information. Remember, venues know the people behind the businesses on their preferred vendor lists. You as their client should feel free to ask them as many questions as you want, it can help you narrow down what vendors you want to interview.