1998 Other Nissan Models what to do

About 1 year ago, in france my engine was overheating.
the local garage took off the cylinder head had it skimmed and put it back together.(It was expensive!)
just recently it overheated again, about 3000 miles later. The same garage, different owner said he would look at it; but he had the head skimmed again but said he wont know what the problem was/is until hes put it back together. Might be leaking radiator or piston rings!
im not rich or mad so what should he have done first, apart from tell me its going to hurt!
please help,
dave