Some are, some aren't.
It's just the same with heart surgeons and car mechanics.
Keep your eye on them, whilst they are working at your home. Don't be frightened of challenging them, if you think they aren't doing the job properly.
And the classic retort will be, "We haven't finished, yet! Come back and check the job when we've finished."
The top tip is, that no matter what terms they want with their order in the showroom, insist that you will only give them an order if the final balance is only due and payable by you, when you have been able to check things out to your satisfaction. If they can't agree to this, then seriously, DO NOT GIVE THEM THE ORDER.