I just noticed this thread. A bit off topic!
Anyway, I've a friend whose got a similar web-site and has recently sacked his estate agents job and does this full time.
There's good money to be made. He waits till he gets a batch of jobs in the same area - mostly requests from Americans - and travels out to the local area.
Before he goes he does his research and he'll only find graves within certain date parameters (something to do with when accurate records started being kept). Before a certain date, 1873 for example, he'll still do a search but before hand advises that the chance of finding the grave is minimal. He still gets paid either way and takes a deposit first.
I don't know how much he makes; but he implies it's well paid and he likes travelling round the place, staying in hotels, with very little work to do.
When he finds the grave he takes a picture of it and supplies local information (history etc) of the area.
It sounds okay to me.