Worries about breakdowns and maintaiance - buy it for 500, if it breaks down, buy another one for 500, if that breaks down, buy another one - and you have spend the same as a new bike, and have lots of spares. Don't spend all your money on the bike (but that applies to a new bike as well), allow some for maintance costs, maybe a bit more, but not much more, for second hand over a new bike.
As the bike is coming from a reputable shop, and you say its in good condition, I would expect it to be as reliable as a new bike. Many bikes get bought and never ridden hard, if at all, so they are hardly used after 7 years. The shop would not stock a worn out bike, and will have serviced it.
As far as ride goes, bikes have changed over the last 25 years since the first full sus became popular, but that change has slowed down significantly. Current models (with same travel suspesion), while better than a 7yo bike, are bit lighter and a bit smoother, but significantly the same. The big difference is suspesion travel has increased as they can make longer travel while maintaining stiffness and reliability with better design and lighter materials. Question is - do you really need 500mm of travel? Can you afford the luxury of a newer, better bike?
Read back at many of my previous answers - I always recommend a second hand bike, if possible from an LBS, for people on a budget and new to riding. The bike described sounds ideal.