Troubleshooting page load time issue only one client is having....

We had a previous page load time issue specific to one client that was tied to wp super cache. We've disabled all caching and we now have a client that is reporting 30 second page load times.

We aren't able to reproduce the load time issue and random page load time tools don't show times out of the ordinary. The issue seems to be specific to this one client. I'm still waiting on a response as to whether the client has tried loading the site in more than one location, but he did indicate all other random websites he goes to do not have page load times.

Anyone have any tips on how to troubleshoot an issue like this that seems to be an isolated issue?