Hi Hannah40 - I dont know anything about shared lives carers but I do foster. The fostering association actually hold tax and benefits sessions so we as foster parents are well aware how to manage our money when it comes to the tax man/ benefits or tax credits. To be honest the tax credit people don't always know the rules, and sometimes I have had to be quite forceful about it, and ask to speak to someone higher up.
As a fostercarer, you can consider yourself either unemployed and claim income support, or in full time employment and claim WTC. There is a set formula for working out your earnings, and the threshhold is quite high, if you earn over a certain amount, it counts as earnings. But you do have to be paid quite a lot of money before you reach this bracket.