I am about to buy a 2000 chrysler sebring convertible 2.5L 6cyl and the peddle is feeling mushy and goes all the way to the floor almost. The guy just replaced the breaks recently and I cannot see any break fluid dripping from the lines or calipers.. should I replace the master cylinder?

 

First thing to do for a soft brake pedal (note correct spelling) is to bleed the brakes. Start with the wheel farthest from the master cylinder and do the wheels in order until you finish with the one closest to the master cylinder. If that doesn't do the trick, you may need to bleed the master cylinder. That's a more complicated procedure but if you look it up you can decide if you are up to the task.
Be aware that with the engine running and the power brakes operating correctly, you will be able to push the pedal all the way to the floor. You don't get a hard pedal until you shut down the engine and pump the brakes a few times to use up the vacuum that is stored in the reservoir.