Is It The Right Size?

• Measure the length of the back.
• 351cm - 359cm is considered to be the safest.
• Some players of large build like up to 363cm.

Either
Brilliant and powerful - can be heard against a grand piano or orchestra

Or
Warm and sweet - quality of sound before quantity

Is It In Good Condition?

• Have any cracks been well restored?
• Is there a soundpost crack or other bad cracks in the back?
• Is there any woodworm damage?
• Is there any sinkage or twisting of the table? If there is, a new bass bar may be needed.
• Is there any repair in the neck?

Is It Authentic?
Don't expect the label to be necessarily correct. The instrument may be a copy of that maker's work, or the label may have been inserted for attempted financial gain, possibly a long time ago.

How Easy Is It To Play?
Try it in different rooms and in a big hall.
It should have a clear sound that is even on all four strings.
The tone should not be shrill or dull, although violins (especially new ones) can improve with playing, they should sound well from the beginning.

New Violins
Well-made new violins can have strength and quality of sound. During the first year of use the tone will further improve, especially if it is played frequently.
New instruments need more adjustment than old ones. Neglect of this may be responsible for the idea, sometimes expressed, that their sound can deteriorate.
However, it is true that some new instruments are made thinly in an effort to make them easier to play. This can usually be detected by sinkage in the table.
The solution is to choose a maker with a good track record.

...A responsive instrument helps us to free our musical imagination and express depth of emotion and dynamic range.