Testing and proving that site slowdowns are not due to server issues

I have a rather vocal web hosting client that has emailed me several times saying that his sites are loading slowly. When I check everything seems fine, loads fast, and none of the other clients are seeing any problems. I run tests with online tools like the Pingdom tools and multi location testers like http://cloudmonitor.ca.com/en/checkit.php and everything says they are fine and running fast.

I have two questions related to this.

First, just in case it is an intermittent thing that fixes itself by the time I check it, is there any way for me to analyze the logs or look for something in the Apache logs, WHM, or at the command line that will tell me if there have been problems in the past few hours?

Second question is if anyone has any suggestions for how to deal with this clients concerns? He is my biggest client and I don't want to lose him. I hate having to tell him every time that it is a problem on his end and not on mine. Sadly he is not very technical and thus does not know how to troubleshoot such things. Any ideas?

 

Well, I'm not that familiar with Apache logs, so I'm gonna skip that part, but as for the sites, it might be prudent to just do an analysis of the sites themselves - do they rely heavily on external resources? Might there be some loading-issues related to being logged in/not logged in? Is the client located somewhere with known issues regarding broadband connectivity? Does the client have a good line?
Does this happen on other sites as well? (Ie, does the client have problems loading several sites, not just his own?)
You could perhaps tell the client to test other sites located on the same server or server farm, and see if there's still a problem. If it is, the problem is perhaps on the client side, if it isn't, maybe there's something about these particular sites that creates the problem.

 

It turns out it was indeed the client's connection. I got on Skype with him and ran him through some tests including doing a tracert through the command line. He was able to see that his path to the server was getting broken due to a bad router somewhere in between. I also had him run a virus scan using eset's online scanner. We found dozens of pieces of malware and toolbar junk on his machine.

 

Hi

1. every web hosting provide set of cpanel tools to track apache logs , error logs and client/server logs . Filter your logs by 400+ status for any client issues and 500+ for server issues

2.Use gtmetrix and find if you can really improve your blog performance

Thanks