I'm still trying to buy a decent second hand Disco, and, like everyone else looking, I'm finding it difficult to find a decent one....

Apart from having a Service history and checking the obvious Disco faults, is there a "rule of thumb" on what not to buy?

Is the "shopping trolley" owner/seller a better buy as it won't have been "enthusiasticaly abused" off road? - I plan to use mine in an environment where it will be used to it's fullest potential.

Are there any definitive "no no's" and tips on what to avoid?

It's a nightmare out there...

I just look in the paper & go and buy the first one I see - having decided by reading the paper which one sounds bestest. Whichever one you buy will go wrong but it's up to you whether that's a real bad thing or just lifes challenge.

FFS just do it - it's only money

really depends on your budget.
if its just for mudplugging, then get a good abused one for about a grand.
at least the TB should work?

If it's going to be little more than a serious off road tool then get a defender instead, much more capable in extreme off roading.