One of the mums at school asked me to do a favour and pick up her DDs after school one day and take them back to mine until she finished work. I agree as I am also a working mum and understand all the difficulties this entails. So then she asks again the next week and the following week and so on so I am now in an awkward position of being informal regular childcare. I have since found out that she has also used some other mums until they have got fed up so I guess I was next in the list. This is not the first time I have ended up in this situation, another mum asked me to drop her DD to school intimating that she had to work, when in fact she was going to the gym 
Don't get me wrong I am happy to help friends out as we all need to get by and more often than not I will also need a favour at some stage. It is after all how us parents without extended family to rely on manage to get by. However, I would never ask a favour under the guise of having to work and then sneak off to the hairdressers or the gym. It is especially grating when you know you could not rely the person in question to return the favour.
Perhaps I am over thinking this but if you have to work then you can't rely on favours as a long term childcare solution. Also it is totally U to take advantage of other working mums good nature by pretending to be in a bind with work while actually swanning off and enjoying yourself. AIBU?