Do it! Buy and sell quality used items whenever you can :)
Around 5 years ago I bought a specialty weight lifting handle new. Maybe a year later I traded it for a specialty dumbbell. A year after that I traded it for specialty lifting books. I just sold those books to get money towards a bigger purchase of lifting equipment. I cleared 1/3 of what I spent on the original handle.
I am a lazy seller and originally bought new, so I took a small loss on each transaction. Paypal got a cut a few times. Another mistake was owning books, since they hold value really poorly.
Yet, for just 66% of what most people would have spent on the first item, I've been able to use several desireable "expensive" items over the years. Making it even better, I am not storing the stuff I got bored of. It's rare a purchase holds my interest after the first 6 months to a year.
Had I entered into the process with a used item, and my rule to "never buy media" been in use back then, I would probably have my entire original purchase amount back.
Admittedly my numbers ignore shipping costs. They did not differ much from what I would have spent new, since all my transactions were online. Local transactions using Craigslist get around this though, and are something I am moving towards. They also have the benefit of eliminating Paypal's cut.
Alltogether though, even with my poor strategy, selling my stuff on the internet let me afford a much higher standard of living with little money. That rocks.