Yes, the room is going to affect sound quality as the others have mentioned. For arguments sake, take notice as to how the demo room sounds in comparision to your room at home. Talk to the salesperson in the room. Is it easy to hear them? hard to hear them? Does the conversation sound dull? Brite? Clap and see if you get echo, sharpness etc. At the least you can make your own assesment without bringing in sound testing equipment to the demo room!
After you hear something you like, ask the dealer if you can try it out at home. Or, do a blind test at a showroom. At least you have a starting point.
How about if you brought in your current receiver to a dealer? Then you can REALLY compare receivers.
Another good point is this: do you listen to 2 channel music on the system? If the answer is yes, then absolutely demo receivers as they all sound good for surround (in that $ range) but some will be MUCH better for good old stereo music. If you are 85% + for surround sound, then I would not be as critical for choosing the receiver.
