Violins are made of wood, and wood is affected by the environment. Because of this it is important to examine the body of any violin (new or used) to make sure that there are no cracks in the top or back.
Well repaired cracks in the top of an older instrument may not be a problem (Seek the advice of a teacher or violin maker), but cracks in the back of an instrument can depreciate its value as much as 75 percent. From my experience, violins ten years old and younger that have repaired cracks, will often be more sensitive to environmental changes such as humidity and temperature, and their sound will be affected quite a lot on some very hot or very dry days. In any case, crack in the violin can start the negotiation on violin price.
Examine the ribs (sides) of the violin to make sure that they are not bulging out beyond the edges of the top or back. This happens because wood that is not well seasoned will shrink noticeably when it dries out. As the top and back shrink, the ribs begin to bulge. Most instruments of reasonable quality do not have this problem, because close attention is given to curing the wood properly. If everything else is in good order, this may not be cause to reject a used violin, but consult your violin repair shop concerning repair costs before making such a purchase. Again, this can be a good reason to negotiate the price of the instrument.
Check to make sure that the neck of the violin is straight. Occasionally an instrument is made wrong, and somehow slips through the adjusting process unnoticed.
Make sure the bridge is centered between the f-holes, then sight up the fingerboard to see if it aligns with the bridge. If the bridge must be offset toward one side or the other to make the strings and fingerboard line up, it will require repair by professional. Make sure that the intervals between the strings on the nut are even.
“Set up” on violins is very important. This includes proper bridge and string nut fitting so that the strings are a proper height from the fingerboard, fingerboard planning to make sure the strings don’t buzz, peg fitting so the pegs turn smoothly and stay in place, and setting the soundpost for proper tone adjustment, etc.
Some music stores do not set up their own instruments, but well-known brands generally are shipped in good adjustment. Many violin shops do their own “set ups,” and work with the customer to meet the requirements of the teacher.
Most violin outfits will have a case and bow included in the price. A fiberglass bow with horsehair is often included in beginners outfits. A wood bow can add $100 or more to the cost of a beginning violin outfit. I have a strong preference for wood bows even for my beginning students. For my opinion, the fiberglass bows don’t feel the same and don’t play the same as wood bows. Even high quality carbon bows are my least preferred choice. The only advantage of synthetic bow is that it wouldn’t get warp if maintained not properly.