certain things to look for.
-3m or Llumar tints
-Lifetime warranty against bubbles or any defects.
-make sure they do the back window as a one-piece.
-The tints are up to the top on the side windows.
-look at the cars they've done.
Price does not reflect quality.
A couple of my boys got their cars done for $100-130 and their tint jobs turned out better than my $150 job.
Just watch them do it and it's better to find a shop recommended by a friend or someone whos had it done than to find any random shops.
good luck