Some personal injury cases are straightforward. Car accidents are a good example. Fairly early on, for little or no cost, you can get a good idea of who was at fault, how the accident happened, and what the injuries are. For the facts of the accident, the police report is usually accurate, or at least in the ballpark. For injuries, you get medical records from the client's doctors.
Others are more complicated. I have a case resulting from a bar fight. The case is against the bar, mainly on the theory that they knew the assailant was behaving in a violent manner and they didn't keep him out or otherwise protect the patrons (including my client, who was badly injured) from him.
So how do you prove the bar knew he was behaving violently? I was thinking about taking another bar fight case. I was contacted by the mother of the "victim". On their description it was a good case.
However (the key word in telling a good story?), a careful personal injury lawyer does not take a case solely on the prospective client's description. In the new case, I told the mom I would only take the case if we first had a private investigator go out and take statements from witnesses -- and mom was going to have to pay the bill (about $500).
I introduced the investigator to the mom, she paid him, and he investigated. The story did not turn out so good for the "victim", and I did not take the case.
In the one I did take, which is getting closer to trial, I did something similar. As appropriate with tricky cases, I made the client put up the initial expenses. You have more confidence in the case if the client shows their belief by putting their money up.