Are they reliable? Many are, some are not, in large part it depends (as it does with most vehicles) upon the maintenance provided and the diligence of the owner to catch any problems early. Ideally you'll be looking for a vehicle that has not had a hard life. Your lucky in that you've come to the right place, if there are KJ problems we know about them. What to look for depends on the model (CRD or petrol). Can you narrow down the field for us? Any idea of what years your looking at? You might want to start by reading through the library of KJ Sticky postings on the Aus Jeep Offroad forum:
Here:
http://www.ausjeepoffroad.com/forum/for ... .php?f=158That reading provides a fairly good KJ education (at least on what can go wrong and what to do to avoid or fix it).
Don't be put off by the topics as people tend to write about the dramas they have had, and you never hear about the tens of thousands of kilometres of trouble free travelling. There are KJs with close to 250000 kilometres on them and still going.