I'm sure it's a tough situation to be in, they need to know enough information to know you're legitimate and to trust you, but give away too much and you've basically drawn the family tree for them. And the added factor that you're basically informing them of a death in the family.
I too saw the lady in the shoe shop programme the other day, that was one where I truly felt sorry for you guys. Purely because without people like you researching it she would have never known.
When it's a family member people knew I can understand, to a degree, going it alone. But when it comes out of the blue like that (the way it came across she didn't even realise the "Auntie" she met just once was her mother's twin!) it's probably worth paying them for the research work.
Neil, do you ever have cases where the person decides to go it alone, but then when they realise how much work will be involved come back to you?