The best clue on whether to buy a particular Auster is probably the stock of spare parts that comes with it!
The last ADs were issued donkey's years ago (apart from inspection of fabric aircraft a latter generic D on all fabric machines). Most of these old ADs should have been dealt with moons ago - but it leads on to the spares.
Brake backplates, particularly the starboard one, are hard to get hold of, anyone who really flies and looks after their machine will have spares, ditto rocker box gaskets, seals for the pushrods, brake shoes.
The metal props are a bit coarse for strip performance but offer good cruising, the belly tank is a near essential unless you live in the south or do not travel any real distance.
The aircraft is very simple and built like an outhouse. There are noisy but honest sort of machines. Try a couple before you buy.
Make sure the Gypsy has had the 'ring conversion' which dramatically reduces oil consumption (for future reference make sure you know which conversion - getting the right replacement rings is a nightmare otherwise).
Remember you'll spend at least as much time re-tightening and claning things as you will flying!!!
Happy landings