Rarely.  Usually the client has been wronged but it would be very costly to litigate the case and the recoverable damages are low relative to the cost of the litigation.  So Ms Client, if you hear a lawyer tell you that you have “no case” ask questions.  Like:

•  Are you telling me it would cost too much to pursue?  Why are you saying that?
• Are you telling me that it’s a bad fit for your office?  Why?
• Might other lawyers be interested in this case?  Do you now any of them?
• Are you telling me that there are problems of proof in the case?

I do sometimes do commercial litigation on a contingency fee. But, also, I do tell potential clients that I’d be happy to take their case if they paid an hourly fee, but that the damages are not high enough, or liability is too speculative, or the defendant is insufficiently credit-worthy for me to take it on a contingency.