I was thinking of buying a Subaru Impreza STi and, not knowing that much about them, thought this small pocket sized guide might be useful. And indeed it was.
Illustrated with plenty of close-up colour photos, it takes the potential owner through a potted history of the cars from 1992 right up to 2007. You then get a detailed series of paragraphs telling you exactly what to look for as you're viewing a car, how to haggle and buying at auction etc.
There's a lot of sensible general advice here which could apply to any car you can think of, but unsurprisingly there's also a lot of very specific information about Imprezas and their foibles. Some items are not covered in particular detail, but note well what the author says and you should end up with a good one.
My only real criticism of the book is it was published in 2008 and is now becoming a little out of date. The last three years and the particularly hard winters we've had (in the UK) will have meant the car you're now looking at, which is probably past its anti-corrosion warranty, could well be suffering from rust.
As a specific warning, during my hunt, I encountered a 2002 car which superficially looked fine, but closer inspection revealed the crossmember and subframe under the driver's side of the engine were corroded to the point of having several large holes in them, despite it having just passed its MoT. The book doesn't tell you anything about this and it could really do with revising to include a lot more about where to look hard for rot. Don't be afraid to ask to have the wheels and the engine undertray taken off to properly look at this. The plastic hid the rot on this car remarkably well.
Subaru parts can be frighteningly expensive and the book covers items such as brakes, clutches and exhausts, the imminent replacement of which could add at least £2000 to the cost of the car you've just bought. Don't disregard the author's advice here as it is very sensible.
So buy this book and take it along with you to view a car. But my advice would be to also take along a mate who doesn't like them. His jaundiced view, coupled with the book, may well save you a great deal of money.