Hi, I'm Kenny Martin at Competition Cars and Classics,

I worked for the New Subaru Dealer in Roanoke for over 15 years before opening up our own car lot. I was a Certified Subaru rep for my last 10 years. You will notice in our inventory we do sell a lot of Subaru's.
Subaru makes a great vehicle, with very high safety ratings, the best all wheel drive system, and typically above average dependability. However, there are things to have checked on your Subaru, if looking to buy used.

Subaru's are well known to have head gasket leaks. While most vehicles head gaskets will typically leak coolant into the oil, Subaru's will normally begin to leak oil externally. 
The design of the boxer engine, with the heads sitting horizontally, makes them always have oil pooling on the edge of the head. Eventually, you may start to see drips of oil in your driveway.
That's a good sign, you may have a head gasket leak. Many times it will start with just a little seeping around the head, but eventually will turn into drips.
The car will be drive able in this condition, but you may begin to smell burning oil, and see the drips on the ground.
This is a good time to have the head gaskets replaced, along with the timing belt and water pump. The timing belt is critical in a Subaru engine. This is an interference engine, and if the timing belt breaks, your engine is pretty much toast. While accessing the timing belt, this is the best time to replace the water pump as well. This preventive maintenance can prevent costly repairs down the road. 
When looking for a Used Subaru, ask about service records. Many dealerships may not have that information, and it will be up to you to verify what repairs and maintenance are needed. I always recommend you take any vehicle to your mechanic before purchasing, to evaluate what is needed.
Timing belts, and head gaskets are not cheap repairs. The dealership will typically be the highest cost to have the repair done.
Many Independent garages can handle this job. Cost will vary tremendously but a head gasket, water pump and timing belt job on a 2.5 Subaru engine, should run no more than $2,000 at an Independent shop. This will vary based on what machine work needs to be done, the shops labor rate, the amount of time they allow for the job and what they charge you for parts.

Some years of Subaru engines are also prone to above average oil usage. Subaru deems it normal to use 1 quart in between oil changes. With any vehicle,checking your oil level should be a priority at every other fuel fill up, but with Subaru, even more so. 

Subaru is a great vehicle. But do expect your maintenance cost to be higher than a normal vehicle. My sons 2010 Forester has around 215,000 miles. We did the timing belt, water pump and head gaskets at around 204,000 miles. I fully expect it to be good to go until 300,000 miles. An expensive service, but much less than buying another vehicle, and we know it's been done.

So when looking at a Used Subaru, get it checked out by a mechanic. It can make you a great vehicle!
When looking to buy a used Subaru, buy form someone with knowledge and experience in the product. 
Competition Cars and Classics is about as close as you will find, to being a used Subaru dealer!