Ask casually about the vendor's touring experience. What you really want is an estimate of the miles on the bike.
It might be a gem... purchased in 2007 and just lightly used. Or it could be a stone boat. If the owner has done 10,000 to 20,000 miles of touring on it, check the components. Replaced parts should be same quality as original, or better. I saw a Miyata 1000 years ago for a reasonable price. From what I could see, it appeared that a husband and wife had bought matching bikes. The husband wore his out and moved all her nearly new components onto his bike. He replaced the wife's components with crap and then tried to sell her bike. The bike was not good value. But don't be too suspicious. Not all vendors are liars .

I hope it works out for you. Make sure it is a good fit... the best bike that is too big or too small is not a deal at all.