And so are French, German, American and Australian workmen!
Every trade has its cowboys, for heaven's sake, and we all remember and bellyache (rightly) about a bad job. Most tradesmen, however, do a bloody good job. So good, in fact, that we don't get to hear about it.
As other people have said here, never employ anyone straight out of the yellow pages - always seek a recommendation. Ask around neighbours, friends and relatives and then employ someone. For smaller jobs, get them to inspect the job and give a written estimate and then only pay when all the work has been examined and tested by him and you. For larger jobs, agree payment schedules and, if necessary, have a penalty clause.
What really is shite about the UK is the system that makes it impossible to get quick redress for a shoddy job. A trade association with the ability to make a tradesman rectify a problem is what's needed - give the corgi teeth!