My questions would be how do I vet those who are serious players from those who aren't doing great numbers?

Think about all the players - seller, you and lender and work creatively to find a win-win-win.  

Start making connections with property managers, realtors, contractors in your target areas, so when you find a potential deal all the players are in place and you can move forward quickly.

Considering all of the players that have to make a profit for what they do, how much below market value do expect to clear? 

Attend meetings to learn the real estate investing vocabulary, find out who is doing what in your area, who the players are, and which vendors your should use (attorneys, insurance agents, lenders, contractors, etc.).You're in college now so you understand the importance of education.

The idea of a lead gen service makes finding motivated sellers SOUND so easy, but I was just at a networking event and talking to a local player who was successful before and after using their service, but said he "lost his shirt" with them. 

I am trying to find out who the "Big Players" in Dallas are.

In no time you'll be slammed with enough keyword alerts to give you a solid idea on the biggest players & markets that are represented by members here on the site.

With institutional real estate investments, the advice of an expert who works in the industry every day, knows all the players and their track records, and performs due diligence on each offering is a great benefit to you and comes to you at no cost.

You will also learn the players in your area who may also be willing to coach/mentor you.