Hi,
I have been using Apache since the mid 1990s. Until a couple of years ago I ran a number of multi-million-page-per-day websites on a set of Linux-based systems. I do know what I'm talking about.
My approach is very simple. I take a look at the problem system, remotely from here. If I can fix it I tell you so and you pay me. If I can't, you pay nothing.
Regards,
Chris