Update: Well, I've tried and tried to convince the owner of Riverside Furniture that their computer is infected, but they're still of the opinion that my anti-virus software is over sensitive. This is because other customers have experienced no problems at all in accessing their site. Also, they say they've tried to access their site on a few other computers, again with no problems.
Furthermore, they have reported all of this to their 'webmaster' (a misnomer?) Amazingly, the webmaster reckons it will be too difficult to find the miscreant code, like looking for a needle in the proverbial haystack! Therefore, they will ignore it (more or less). And yet, you wizz kids here found the problem within minutes, maybe even seconds!
I've heard back from Avast technical support. They will review the infected site in the Avast 'laboratory' and will remove the Trojan warning if it turns out to be a 'false positive'.