Since I've been burned by bad contractors lately, here's some consumer tips.

With any contractor, be sure to check out the following:

Better Business Bureau complaint records (also find out if they're a
BBB member)
http://www.stlouis.bbb.org/search.html

Secretary of State business entities (does the business really exist?)
http://www.sos.state.mo.us/BusinessEntity/

Plumbing and electrical - do they have a City of St. Louis license?
They are supposed to say so in their advertising. But confirm by
calling (314) 622-3325 (City Building Div Electrical Section) or
(314) 622-4356 (City Building Div Plumbing Section).
http://stlouis.missouri.org/government/building.html

Do a Google search for their name (+city, if
necessary) to see if anything comes up. You never know what you might
find.