So the piano you got on Craigslist doesn't REALLY play that well?
As Texas Gov. Rick Perry would say, "Oops!"
Well, it happens to the best of us.
Here's a plan to "unscrew" that piano problem. Contact your local piano technician request a piano repair estimate. More often than not, the best course of action is to plan on paying to have your piano tuner come out to your house, open up the piano and find the problem. It's well worth the money. Most tuners will do this for around $100. If the problem is a minor in nature, the technician may offer to stay and repair the piano and then tune it on the spot without charging you for an estimate. This is the best scenario, so take advantage of it.
If the piano needs major repairs, you should ask what the charges for an inspection, appraisal and repair estimate. Many pianos need action overhauls, string repairs or key repairs which can give the piano a new life. These repairs usually run several hundred dollars. Have piano inspected to get a list of the repair problems, get an appraisal to find out what it's worth and a repair estimate to find out exactly how much it will cost to bring it up to speed. Pianos are like cars; when they need major repairs, you need to make a decision as to whether or not they are, in fact, "economical to repair."
The Reality Check Part:
Don't just let the piano sit there. Sometimes, pianos cannot be repaired unless completely rebuilt costing thousands of dollars. Most often, free and cheap pianos found online usually cost a few hundred of dollars to fix, so "bite the bullet" and plan on paying for a repair estimate. Then schedule your piano technician fix it and you will be playing, "I Can See Clearly Now" in no time.