I turn cases down for either or both reasons: Because they lack merit and/or because I don't want to spend the money and time on a case I see as having a low probability of success even if the potential client has a legitimate claim.

I will say too though, that I have taken on a lot of these cases that, in retrospect, I should have stayed far away from. I stick with these cases though because the client is counting on me. I have a case going to trial in August that I never should have pursued. I think my client has a legitimate claim but it will be a very difficult case to prove.

It's an inexact science.