General rule is to stay well clear of any "tradesmen" calling to the house offering their services. If at all possible, look for recommendations from friends & neighbours.
Failing that, look up a number of companies in the Golden Pages and the like, and try to assess which are reputable and which are not. Most trades will now provide free estimates for any such work, when they call, try to have a few questions ready for them, and use their responses to help you choose.
Always look for a land line, at least then you have some hope of tracking them down, through the courts if necessary. If they're only prepared to give you a mobile number, chances are they'll just ignore you in the event of problems, and pay-as-you-go phones are generally untraceable!
I previously bought a house from a builder who never answered his phone, but usually phones back straight away after listening to the message I left. A while later the sheriff’s office called looking for him, they had something like 4 mobile numbers for him, but he never returned their calls...
Back to your particular problem, there are many companies around doing PVC facia and guttering, it's not beyond a competent DIY'er to put up.
Leo