Earlier quoted context omitted.
Further, when I hire someone to fix my roof, I don't make him build me a doghouse first to scrutinize whether he's any good. On the other hand, if you don't ask at least some basic questions, you risk hiring the Brillant Paula Bean [1]. 1: http://thedailywtf.com/articles/The_Brillant_Paula_Bean
I kind of wish I'd gotten the people I hired to build our terrace to first build something small, like a doghouse, before hiring them.
Another way to get a good contractor (in the first place) is to ask around via a somewhat orthogonal method. For instance, we needed to get a new block fence installed around our house. This wasn't going to be cheap, and we wanted it done right. My wife interviewed several contractors, and half of them were drunk, and the other half couldn't figure out which end of a tape measure to use.
So we got creative: "Who should we call that might know who is a good contractor for block fence construction, and who isn't?"
Well - that's the kind of thing you have to go "inside" the industry; so we figured, well let's call some suppliers of concrete block. A few calls around to these places, asking the people "who would you hire to build a fence" produced a list of candidates from each vendor - and where there were matches, that boosted them on the list. Narrowed it down to three, had them come out and bid, then we went with the guy who struck our fancy best (not with the cheapest - never go with the cheapest, unless they seem the most competent).
We've used this kind of system since (along with checking references and such), and haven't had a problem finding a capable contractor for construction and maintenance work.