I'm not familiar with the characteristics that are particular to classic guitars. I offer some things I look for in steel-string acoustics.

-Thump several places on the body with the side of your thumb. Don't use your finger tip, because you do not want to scratch the finish with your nail. There should be no hint of buzzing sounds which would indicate that something is loose.

-Inside the guitar is where the attention to detail, (or lack of it), shows up. Get an inspection mirror at a hardware store or a car parts store. This is a bigger version of the kind of mirror a dentist uses. These things are handy for checking the inside of a guitar. Poke it into the sound hole and take a look around. The glue joints should be neat and tidy... no gaps or globs of sqeeze-out. Any cracked braces are cause to leave the guitar in the shop, and move on.

-Look closely at everything! Glue joints at the bridge and neck should be free of gaps or squeeze-out. Marquetry should be smooth and crisp, no decals! The tuners should operate smoothly. The strings should sit no more than half-way into the nut. The ends of the frets should not have any sharp edges. There should be no 'belly' on the body (caused by tension on the bridge pulling the top of the body outwards). The neck should be straight and flat, no twist, and only a very little bow.

-If you're still interested in it, you can play. By now, you should already know what kind of sound you are seeking. A good guitar will deliver this. A great guitar will come alive in your hands. If you can possibly afford it, find youself a great guitar! Save up while you look for it. May your search and your savings come together for you.