As for whether or not you should use a broker, I would suggest yes, especially in the current climate.
As for how to know if you can trust the broker, it is difficult to tell and a referral from a friend is one way of finding one. A possible idea is to call them up and see how you feel. One point to note is that if you are remortgaging, a good broker will ask you to go to your current lender and see what they are offering, as if there is nothing better than that there is no point in moving you. So see if the advisor asks you that question first, if not, they aren't offering you the best advice and you may wish to avoid them.
I am an independent
mortgage broker and the first thing I suggest to anybody remortgaging is to see their current lender first. That gives us a benchmark to aim for, and if we can't improve on that then I suggest they stay where they are.
Hope that's helpful.