Tips on buying lollapalooza tickets from a private seller?

hey everyone! this will be my first year attending lollapalooza and i'm checkin the website and not suprisingly the tickets are sold out. so i'm going to have to resort to a different site to buy tix from a private seller. any tips on this? should i be looking for a certain type of ticket or is 'general admission' ok? just want to make sure i'm getting the best deal/ticket for this noob buyer ;) if anyone has any other tips (besides lollapalooza sucks don't go!...) that would be awesome. thanks guys! :D