I know how you feel, I just bought my first car and I hate taking it to garages as I have no way of knowing if they are taking the p*ss or not. Still, when I bought it the first thing I did was get a full service. I took it to a Nationwide Autocentre cause I got a discount. The point it is, if my memory serves correctly they charge £50 for "diagnostics" (which may be knocked off the cost of repair if you choose to use them, or it may not, i forget) and offer a guarantee which basically says "If we fix the wrong thing they will refund the cost of the repairs"

Which gives you some peace of mind at least. Maybe suitable to someone in your situation?