Getting back to Frasbe's question, this year I asked the Mechanic If he would only do a habitation check and not bother with the Brakes, as we have only done about 500 miles, he was happy saved me £50, and stamped my Service book with Habitation check done. I am happy with that.
If I was buying the said caravan and someone had stamps for Bi annual servicing, I would look at damp reports and if all were good then a sale could be done.
I know a forum member that always does his own servicing, why not.