I'll chime in since I build a lot of wheels.
Anyone can build wheels once they memorize the lacing pattern. It took me What determines a good wheel is the attention to detail. before you commit to a builder ask a few simple questions, and if they can't answer them with confidence you know he/she is just an "Average" builder. Just like you obsess over the details of who builds a better hub, you need to have the same fine grain filter for the guys building your hoops.
Don't buy a wheel if the guy is using blue threadlocker on the spoke threads. That's just hackery. I'm just saying, I've seen it done a lot and it is embarrassing. I use Wheelsmith Spoke Prep. Expensive stuff compared to linseed oil (which works well too), but the blue/pink colors really help make sense of a bundle of spokes if you're building a lot of wheels like we do.
http://www.wheelsmith.com/ourtools.html
Make sure they have a dishing gauge, and a Park Tool 1554-1 centering gauge. Both of these relate to the dish of the wheel, but the latter makes sure that the builder's stand is perfectly true before the build even starts. It is a solid block of steel that needs to be put into the stand before EVERY wheel build to make sure the stand isn't drifting out of true.
I like to use Morningstar's feeler gauges:
http://morningstartools.com/rims_center.html Accurate to .001", you can build a seriously perfect wheel with these.
Another must-have is a tensiometer. Park makes a really cheap and effective one, but I upgraded 2 years ago to the uber-expensive DT Swiss version:
http://www.dtswiss.com/Products/Proline/DT-tensio-analog.aspx I could write a book about this, but there are already many out there... the point I need to drive home is that tension is everything. End Of Discussion. You can build a perfectly true, perfectly round wheel, and then have it fall apart on you because the tension was not part of the builder's focus. since you're balancing a wheel with 32 (or less) spokes, 1 spoke can be way over tension and over-compensate for another spoke on the same side that is way way under tension. The wheel will be true, but the over tensioned spoke will fatigue faster, and the under tensioned spoke will loosen quickly. Neither is good.
My anecdote in regards to this was I had a good friend build me my first set of handmade wheels many years ago. He had built a lot of wheels for people in the past. Why should I question the quality of these perfectly round and true wheels? After an initial break in period of 3 weeks, he trued them again and sent me off to the 24 hrs of Allamuchy, where i was to do my first solo. around midnight, slogging up a muddy hill I said "Before I quit, check the brakes, they aren't dragging... its you. But check any way." I checked and my wheels were literally falling apart.
Blue threadlocker. That stuff was never engineered to hold threads that get adjusted frequently. Also, he never checked tension.
Long-winded, but I'm pretty passionate about this stuff.