Used M.Logans-What to look for?

I'm not certain what you mean by "what to look for." I assume you know what they sound like since you want to purchase them. I assume you know that you need ample space (at least 4 - 5 feet) behind them and no rack or equipment between them. I assume you know that electrostatics need a fair amount of power to sound their best. If you want to know what models to buy, I really like the Prodigees. You see them for sale here about 6 times a year for around $6K - $7K. If you are looking for smaller ML's, the Arius are really sweet too.

Look for dust. If you see a lot of dust on the speakers it could be a problem down the road. Look for pin holes potentialy poked by an animal or child. Otherwise the are pretty rugged.

If you are buying SL3 or reQuest make sure you check the binding posts. They have a tendency to get lose inside. It may not be a big deal if you know how to open up the back cover and tighten them.