Depending on your budget, but you really want to check for some references from the installer. Even small guys who haven't done a lot still should have some references available to you.
Keep in mind that in theory, the A/V installation should be able to be rolled into your mortgage.
For my setup (a dozen + rooms of wiring) it was about $3,000+ for the actual wiring. I consider what I got a bargain.
But, picking someone depends greatly on their experience and sitting down to talk to them for a while. Don't ask them to jump through a lot of hoops for you though, like designing a complete system, if you really don't ever intend to use them. Just be upfront that you are shopping out the competition and want to see how they compare.
You should be able to narrow it down to 2 or 3 that you feel comfortable talking to and working with, then check their references, and maybe see an install or two, then make a decision.
EVERY install, from every company is something of a crap shoot because the builder may be difficult, suppliers could introduce issues, labor could suddenly be tough.
A little patience goes a long way to a better system.