The setup on a fiddle matters more than the fiddle. A modest instrument that has been properly set up will play in tune, respond to a beginner's bow, and stay where you put it; an expensive one that nobody has adjusted since it left the factory will do none of those things and you will blame yourself.
What "set up" actually means
Four things: the bridge shaped and standing in the right place, the soundpost positioned, the pegs fitting so they turn smoothly and hold, and the string height low enough to play without fighting. A shop doing this properly spends real time on it, which is most of what separates a shop instrument from an online one at the same price.
Fine tuners on all four strings are worth asking for as a beginner. Tuning a fiddle by pegs alone is a skill, and spending your first months unable to get in tune teaches you nothing except frustration.
Size and fit
A full-size instrument is standard for adults; smaller fractional sizes exist for children and are measured by arm length rather than age. Too large is worse than too small — a hand stretched to its limit cannot hold a first-position frame without tension, and tension is the thing every teacher spends years undoing.
The bow is half of it
Beginners routinely spend everything on the instrument and take whatever bow comes in the case. That is backwards: the bow is what actually makes the sound, and a straight, properly haired bow of moderate weight will improve a cheap fiddle more than an upgrade of the fiddle would. See rosin and bow care for keeping it working.
Fiddle or violin, concretely
If you already know you want to play traditional music, say so in the shop. The register difference is real at setup time — bridge curvature in particular — and it is far easier to ask for at the start than to change later.